Specification
A FASTENER DEVICE, AN ASSEMBLY OF TWO PARTS ASSEMBLED
TOGETHER BY SUCH A DEVICE, AND A LIFTING UNIT OF A SHED-
FORMING MACHINE COMPRISING SUCH AN ASSEMBLY
In the field of shed-forming, it is necessary to
assemble together certain component parts of heald frame
lifting units of a machine while the machine is being
fabricated. A lifting unit is subjected to high levels
of acceleration and vibration and it also needs to be
compact, of a size complying with the division size of
the loom. For example, FR-A-2 899 602 shows a rotary
dobby in which a cover is fitted on an eccentric and
holds selector members in place. The cover is held on
the eccentric by means of screws. Given the above-
mentioned vibration and acceleration, such screws are
liable to loosen progressively while the dobby is in use.
Similarly, tabs provided with serrations for co-operating
with a locking arm, are likewise held on the eccentric by
means of screws that can loosen while in use.
Nevertheless, assembly using screws is advantageous
compared with assembly using rivets, insofar as there is
no need to use a specific press installation.
Furthermore, the use of a thread-locker composition is
not recommended since disassembling the shed-forming
machine would damage the assembled-together parts.
Furthermore, the thread-locker can degrade over time,
given the working environment of the machine, in
particular because certain parts are located in a bath of
oil and/or work at relatively high temperatures.
In a field other than shed-forming, US-A-5 606 753
discloses making a fastener device by means of a screw
having a hexagonal head associated with a hexagonal
washer that forms a seat and that is provided with tabs
that extend radially outwards relative to side partitions
of the washer, thereby leading to relatively large radial
size for the device and putting a limit on the flexing
length of the tabs. The tabs are subjected to high
levels of flexing stresses during tightening of the
screw. The screw is driven by means, of a key that might
damage the tabs. That device is thus not suitable for
assembling together two component parts of a shed-forming
machine.
Those-are the drawbacks that the invention seeks
more particularly to^ remedy, which invention proposes a
novel fastener device that is more reliable and easier to
implement than those of the state of the art.
To this end, the invention relates to a fastener
device for assembling together at least two component
parts of a shed-forming machine, the device comprising a
screw having a threaded shank and a head having at least
one pair of two adjacent sides forming a non-flat angle
between them. The device is characterized in that:
• the head is provided with a socket for receiving a
tool for driving the screw in rotation; and
• a lock ring is mounted around the screw and
comprises an annular portion bearing against a face of
the head that is facing towards the shank, together with
at least one tab having a first portion facing a first
side of a pair of sides in a radial direction relative to
a central axis of the screw, and having a second portion
facing the second side of the pair of sides in a radial
direction relative to the central axis of the screw, said
second portion of the tab being suitable for moving
towards or away from the second side of the pair of sides
by elastic deformation of the tab.
By means of the invention, it is possible to drive
the head of the screw using the socket, i.e. without
interfering with the outside of said head, which can then
be used to interact over a major fraction of its axial
height with the elastically-deformable tab(s) of the lock
ring. Since the or each tab bears against a first side
of a pair of sides and is capable of moving towards or
away from the second side, when the fastener device is
used for securing two parts together, it need not project
radially significantly outside a circle in which the
shape of the head is inscribed and that is tangential to
the periphery of said head, thereby ensuring that the
device of the invention is radially compact.
According to aspects of the invention that are
advantageous but not essential, such a fastener device
may incorporate one or more of the following
characteristics, taken in any technically feasible
combination:
• The axial height of the tab measured parallel to
the central axis of the screw has a value that is greater
than 50%, preferably greater than 70%, of the value of
the axial height of the head measured parallel to the
central axis of the screw.
• The head is provided with at least two pairs of
two adjacent sides arranged within the circle and forming
non-flat angles between them, while the lock ring is
provided with at least two elastically-deformable tabs
suitable for bearing, via their first portions, against
respective first sides of the pairs of sides, and having
second portions disposed radially facing second sides of
the pairs of sides and suitable for moving towards or
away from said second sides by elastic deformation of the
tabs. Under such circumstances, the two tabs or two of
the tabs are advantageously of different lengths.
• The first portion of the or each tab bears against
the first side of the or each pair of sides.
• A shoulder is formed around the shank on the side
of the head that faces towards the shank, and the lock
ring is mounted around said shoulder.
• The first portion of each tab of the lock ring
forms an angle relative to a face of the annular portion
facing said tab, where the angle is less than 90°. This
enables the lock ring to be snapped onto the head of the
screw and makes it easier to put the screw fitted with
the lock ring into place.
• The first side of each pair of sides is tapered,
converging towards the central axis of the screw away
from the shank.
• The free end of the or each tab is provided with a
chamfer on the side of said end facing towards the
annular portion. This makes it easier to place the screw
fitted with the lock ring in a setback.
The invention also provides an assembly of at least
two parts assembled together by a device as mentioned
above, wherein one of the parts is provided with a
setback for receiving the head and the lock ring, while
the peripheral side of the setback is provided with
serrations receiving an elastically-deformable tab
pressed thereagainst.
Advantageously, a first face of each serration is
suitable for receiving a free side of the or each tab in
locking thrust thereagainst when the screw turns in an
unscrewing direction relative to the part fitted with the
setback.
Finally, the invention provides a heald frame
lifting unit for a shed-forming machine, the jack
comprising at least one assembly of assembled-together
parts as mentioned above.
Such a lifting unit is strong, while still being
suitable for dismantling and it does not require a
specific riveting press to be used while it is being
fabricated. Such a lifting unit may present a thickness
that is compatible with the division size of the loom.
The invention can be better understood and other
advantages thereof appear more clearly in the light of
the following description of an embodiment of a fastener
device, of an assembly of parts, and of a lifting unit of
a shed-forming machine in accordance with the principle
of the invention, given purely by way of example and with
reference to the accompanying drawings, in which:
• Figure 1 is a fragmentary face view of a rotary
dobby lifting unit incorporating the invention;
• Figure 2 is an exploded perspective view of the
portion of the lifting unit that corresponds to detail II
of Figure 1;
¦ Figure 3 is an end view of a screw used in the
lifting unit of Figures 1 and 2;
• Figure 4 is a section view of the screw on line
IV-IV of Figure 3;
• Figure 5 is a view on a larger scale showing a
detail V of Figure 1;
• Figure 5 is a section view on line VI-VI of
Figure 5;
• Figure 7 is a perspective view of a fastener
device in accordance with the invention used on the
lifting unit of Figures 1 to 5; and
• Figure 8 is an exploded perspective view seen from
a different angle and on another scale, showing the
device of Figure 7.
The portion of a heald frame lifting unit 2 shown in
Figure 1 includes an eccentric 4 having the opening of an
oscillating connecting rod 6 mounted freely thereon, with
a ball bearing 8 interposed between them. The connecting
rod 6 is for connection, by means (not shown) including a
pivot arm, to a pulling mechanism that engages a heddle
frame. A main shaft 10 driven with intermittent rotary
movements, stopping every half revolution, is constrained
to rotate with a drive disk 12. Latches 14 and 16 that
are controlled in known manner are provided to secure the
eccentric 4 selectively to the disk 12, depending on the
movement to be imparted to the heddle frame. The latches
14 and 16 are retained on the eccentric 4 by means of a
plastics material cap 20 that is pressed against the
eccentric 4 by two fastener devices 40 that are shown in
greater detail in Figures 2 to 7. Two guide parts 22,
commonly referred to as "ramps", are interposed between
the cap 20. and the eccentric 4 and they project radially
out from the cap, so as to enable them to exert a radial
separation force on the tip of an oscillating lever (not
shown) that is controlled by a reader device, in a manner
analogous to that described in FR-A-2 899 602.
Each fastener device 40 comprises a screw 50 with a
threaded shank 52 and a head 54. The head 54 is provided
on its face 542 facing away from the shank 52 with a
hexagonal socket 56 enabling a matching tool of the male
hexagonal key type to turn the screw 50 about its
longitudinal axis X50,which is the central axis of the
shank 52.
As can be seen more particularly in Figure 3, the
head 54 in.cross-section perpendicular to the axis X^q
presents a shape defined by its periphery 544 that is
inscribed within a circle C50 that is centered on the axis
XjQ and that is of radius R^g equal to the maximum distance
between the periphery 544 and the axis X^g- The circle C^q
is thus tangential to the periphery 544 and centered on
the axis Xjg. The periphery 544 is made up of a plurality
of unit sides, including two circularly arcuate sides
5441 and 5442 centered on the axis X^g and of radius R^g.
The periphery 544 also has two pairs of rectilinear sides
5443 & 5444 and 5445 & 5446. The sides 5443 and 5444
form a pair of adjacent sides disposed between the sides
5441 and 5442, whereas the sides 5445 and 5446 form a
pair of adjacent sides disposed between the sides 5441
and 5442 and opposite the sides 5443 and 5444 relative to
the sides 5441 and 5442. In other words, the head 54 is
symmetrical about a straight line D54 extending radially
relative to the axis Xjg and passing through the
respective middles of the sides 5441 and 5442.
The sides 5443 and 5444 form an angle a;^ between
them, whereas the sides 5445 and 5446 form an angle a.2
between them. The angles a^ and ttj are not flat in the
sense that they are of values other than 0° or 180°. In
practice they have the same value, specifically 130°.
Nevertheless, the angles a;^ and aj could have values that
are different.
The connection radius between the sides 5443 and
5444, and similarly between the sides 5446 and 5445 is of
the order of 15 millimeters (mm) for a screw having a
head with a maximum radius Rjg of 20 mm.
The invention is equally applicable when the sides
5443 to 5446 are not rectilinear, providing the
respective mean directions of two adjacent sides form a
non-flat angle between them.
The screw 50 is also provided with a shoulder 58
that extends around the shank 52, axially between the
shank 52 and the head 54. In cross-section, the shoulder
58 has a periphery 584 with two unit sides 5841 and 5842
in the form of circular arcs and two parallel and
rectilinear unit sides 5843 and 5844. The sides 5841 and
5842 are centered on the axis X^g- The sides 5843 and
5844 are parallel with the sides 5444 and 5445
respectively.
The fastener device 40 also comprises a lock ring 60
made of spring steel and comprising a plane annular
portion 62 defining a central opening 63 that is
generally complementary to the sides 5841 to 5844 of the
shoulder 58, such that the ring 60 can be placed around
the shoulder 58, bearing against the face 546 of the head
54 that faces towards the shank 52, the ring then being
prevented from turning relative to the screw 50. The
ring 60 also has two tabs 64 and 66 that are formed
integrally with its portion 62 and that are connected
thereto via two curved portions 642 and 662 respectively,
such that each tab 64 and 66 forms an angle P of less
than 90° relative to the face 622 of the ring 60 that is
to press against the face 546, the angle (3 being equal to
80°, for example.
The tabs 64 and 66 are plane before the ring 60 is
mounted on the screw 50. Each tab 64 and 66 is provided
with a chamfer 646 or 666 in the vicinity of its free end
644 or 664, on the side of the tab that faces towards the
portion 62. ,
The lengths of the tabs 64 and 66 are written Lg^ ana
Lgg, respectively. The values of the lengths Lg^ and Lgg
are different from each other.
The height of the tab 64, as measured parallel .to
the axis Xjq in the assembled configuration of the ring 60
on the screw 50, is written Hg^. This height is measured
between the face 622 of the portion 62 and the side 647
of the tab 64 opposite from the portion 62. In the same
manner, the axial height of the tab 66, as measured
parallel to the axis Xjq in the assembled configuration of
the ring 60 on the screw 50 between the surface 622 and
the side 667 of said tab that is opposite from the
portion 62, is written Hgg.
-The axial height of the head 54, i.e. the dimension
of said head measured parallel to the axis X^g/ is
similarly written H54.
The values of the axial heights H54 and Hgg are
greater than or equal to 50% of the value of the axial
height H54. In practice, the axial heights Hg^ and H-^g
represent 70% to 100% of the value of the height H54.
Provision can be made for the height H54 to be 0.1 mm
greater than the heights Hg^ and Hgg.
The sides 5444 and 5445 of,the head 54 taper and
converge going away from the shank 62. In other words,
the-unit sides 5444 to 5445 come closer to the axis Xjq on
going away from the shoulder 58. The angle formed
between one of the sides 5444 or 5445 and the face 546 is
written 6, which angle is measured in the material of the
head 54. The values of the angles p and 5 may be equal.
The fact that the angles P and 8 are less than 90° makes
it possible to snap the ring 60 onto the screw 50 by
resiliently engaging the tabs 64 and 56 around the head
54, and more precisely by the tabs 64 and 66 clamping
against the unit sides 5444 and 5445.
In a variant, the angle 8 may be equal to 90°, i.e.
the sides 5444 and 5445 do not taper. Under such
circumstances, the fact that the angle p is less than 90°
enables the ring 60 to clamp resiliently on the head 54.
To make it easier to snap the ring 60 on the screw
50, respective chamfers 5447 and 5448 are provided at the
junctions between the unit sides 5444 and 5445 with the
face 546.
When the ring 60 is mounted on the screw 50, a first
portion 648 of the tab 64 faces and presses against the
unit side 5444 in the radial direction relative to the
axis Xjg, while a second portion 649 extends at a distance
from the unit side 5443. In the same manner, a first
portion 668 of the tab 66 faces and presses against the
unit side 5445 in the radial direction relative to the
axis X50, while a second portion 669 extends at a distance
from the unit side 5446.
The bearing of the first portions 648 and 668 of the
tabs 64 and 66 against the sides 5444 and 5445
respectively enables the ring 60 to be locked effectively
on the screw 50 against rotation about the axis Xj^.
The second portions 649 and 669 extend respectively
facing the sides 5443 and 5446 in radial directions
relative to the axis Xj^ such that these tabs can move
towards or away from these sides to a greater or lesser
extent by the tabs 64 and 66 deforming elastically.
The respective free ends 644 and 664 of the portions
649 and 669 of the tabs 64 and 66 may therefore be at a
greater or smaller distance from the sides 5443 and 5446.
The free sides of each of the tabs 64 and 66, i.e.
their free end sides 644 and 664 that extend
perpendicularly to the portion 62 and that are furthest
from the curved portions 642 or 662, are referenced
respectively 643 or 663.
When the ring 60 is engaged on the screw 50, it is
possible to screw the screw 50 into tapping 41 provided
for this purpose in the eccentric 4, with the shank 52
passing through the cap 20 and through a ramp 22. The
cap 20 is provided with a setback 202 having an end wall
with a circular orifice 204 centered on an axis X204 and
in which the shoulder 58 can be engaged.
In practice, as shown in Figure 1, the cap 20 is
provided with two setbacks 202, since two fastener
devices 40 are used for holding it on the eccentric 4.
In order to enable the ring 60 to be introduced into
the setback 202, the portions 649 and 669 of the tabs 64
and 66 are deformed elastically towards the unit sides
5443 and 5446, i.e. towards the axis Xjq, so as to bring
their second portions 649 and 669 respectively closer to
the sides 5443 and 5446 as represented by arrows Fg in
Figure 2, thus reaching the configuration shown in
Figures 2 and 5. The chamfers 646 and 666 make it easier
to place the ring 60 in the setback 202 by sliding over
the tops of serrations 208.
The value of the connection radius between the edges
5443 and 5444 and between 5445 and 5446 makes it easier
for elastic deformation to take place between the
portions 648 and 649 of the tab 64 and correspondingly of
the portions 668 and 669 of the tab 66.
The peripheral wall 206 of the setback 202 is
provided with fifty serrations 208 that are regularly
distributed around the axis X204 and each of which is
inclined relative to a radial direction relative to the
axis X204 • More precisely, each serration 208 is defined
between two inclined surfaces 2082 and 2084. The base of
a surface 2082 is defined as its junction line with the
adjacent surface 2084 of the same serration, radially on
the outside of said surface 2082 relative to the axis
X204. Likewise, the base of a surface 2084 is defined as
its junction line with the adjacent surface 2082 of the
same , radially on the outside of said surface 2084. In
practice, the bases of the surfaces 2082 and 2084 of a
serration 208 are formed by the same junction line. The
first surface 2082 of a serration 208 forms an angle y^
relative to a radial straight line A;^ passing through its
base, the angle y^ having a value of about 10°. The
second surface 2084 of a serration 208 forms an angle Y2
with a radial straight line Aj passing through its base,
where the angle Y2 is equal to about 80°. The direction
of the inclination of the serrations 208 about the axis
X204 is such that when the screw 50 fitted with the ring
60 is screwed in the direction of arrow F^^ in Figure 5,
the ring follows the rotation of the screw and the
radially outer faces of the ends 644 and 664 of the tabs
slide over the second surfaces 2084 of the serrations 208
until the screw is tight in the tapping 41.
Since the tabs 64 and 66 are deformed elastically by
moving the portions 649 and 669 temporarily closer to the
sides 5443 and 5446 in order to place the ring 60 in the
setback 202, the free ends 644 and 664 are urged under
the effect of the elasticity of the tabs 64 and 66
towards the serrations 208.
If the screw 50 tends to unscrew relative to the
eccentric 4, i.e. to turn in the direction of arrow Fn in
Figure 5, then one of the free sides 643 and 663 of the
tabs 64 and 66 will come to bear against the surface 2082
of one of the serrations 208 under the effect of the
elasticity of the tabs 64 and 66, which surface presents
an inclination that then prevents the ring 60 from
turning, and thus prevents the screw 50 from turning in
the unscrewing direction.
In other words, once it has been put into place in
the setback 202, the ring 60 allows the screw 50 to turn
about the axis X204 in the screw-tightening direction
represented by arrow F^^ in Figure 5, but prevents it from
unscrewing in the direction represented by arrow Fj.
In the example shown having fifty serrations 208
regularly distributed around the side 206, the angle
between two successive serrations 208 is 7.2°, which
corresponds to the maximum loosening stroke that can be
followed by the screw 50 before one of the sides 643 or
663 comes to bear in locking manner against one of the
surfaces 2082.
. Because the lengths Lg^ and Lgg are different, the
free sides 643 and 663 of the tabs 64 and 66 are brought
to bear in locking manner against one of the first faces
2082 of one of the serrations 208 for rotations of
different angular amplitudes of the screw 50 about the
axis X204, thereby further limiting the potential angular
stroke over which the screw can unscrew before it becomes
locked by the ring 60 interacting with a serration 208.
As can be seen more particularly in Figure 6, the
shoulder 58 comes to bear via its surface 582 opposite
from the head 54 against the steel ramp 22, such that by
selecting an appropriate depth Cjo for the setback 202 and
an appropriate axial height Hgg for the shoulder 58, there
is no risk of flattening or plastically deforming the cap
20 when tightening, the screw 50. It is thus possible to
make cap out of plastics material. Thus, the shoulder 58
enables the clamping force due to the screw 50 to be
applied solely against solid parts such as the ramp 22
and the eccentric 4. The presence of the shoulder 58
causes the'clamping force on the cap 20 between the face
546 of the head 54 and the ramp 22 to be relatively
moderate, with the same applying to the clamping force of
the annular portion 62 of the ring 60 between the face
546 of the head 54 and the end wall of the setback 202.
The ring 60 is thus merely "clamped" without being
deformed.
The assembly obtained by means of the screw 50 and
the ring 60 is reversible, insofar as it is possible to
act on the portions 649 and 669 of the tabs 64 and 66 so
as to disengage them from the serrations 208 by urging
them towards the axis X50, e.g. by means of a screwdriver,
while exerting an unscrewing force on the ring 60.
The fastener device of the invention enables great
reliability to be obtained in holding the screw 50 in a
tight position without being influenced by vibration and
without depending on the coefficients of friction between
the head of the screw and the surface against which it
bears. There is no need to have recourse rivets and to a
riveting press for making the assembly. Since the tabs
64 and 66 are disposed along the axis X50 level with the
head 54, they do not increase the length of the screw 50,
so it is possible to comply with the division size of the
loom,' i.e. about 10 mm or 12 mm, constituting the
thickness of the volume available for each heald frame
lifting unit, which thickness is equal to the thickness
of the heddle frames.
In practice, the heights Hg^ and Hgg are slightly
smaller than the height H54 so as to limit any risk of
catching an adjacent lifting unit while the dobby is in
operation.
Since the shape of the head 54 is inscribed within
the circle C50, the tabs 64 and 66, which are curved
towards the inside of the circle when a device 40 is in
its utilization configuration, do not significantly
increase the radial size of the screw. Since the male
key does not interact with the periphery 544 of the head
54, driving the screw by means of a male key does not run
any risk of damaging the tabs 64 and 66, and the tabs may
extend over a height Hg4 or Hgg that is relatively large
compared with the height H54, i.e. greater than 50% and
preferably greater than 70%, thereby imparting good
mechanical properties to the tabs, which are effective in
withstanding the bending and buckling forces to which
they are subjected.
Since the lengths Lg4 and Lgg of the tabs are
relatively great compared with the diameter of the circle
CjQ, the flexing stresses on the tabs are not intense.
This can be assimilated to the fact that the portions 649
and 669 extend over about half of the lengths of the tabs
64 and 66.
In a variant of the invention that is not shown, the
tabs 64 and 66 may be bent plastically towards the sides
5443 and 5446 while the ring 60 is being put into place
on the screw 50. This prior bending of the tabs is such
that they need to be bent still further, in elastic
manner, when they are put into place in the setback.
In another variant of the invention that is not
shown, the portions 648 and 668 of the tabs 64 and 66 do
not bear against the sides 5444 and 5445, but are placed
facing and, at a distance from said sides in a direction
that is radial relative to the axis X^g- Under such
circumstances, the two portions 648 & 649 and 668 & 669
of each tab can move towards and/or away from one of the
unit sides 5443 to 5446 in a direction that is radial
relative to the side mounted facing it, as a result of
elastic deformation of the tabs 64 and 66. This
construction makes it possible to use flexing of the tabs
64 and 66 over a considerable length, practically equal
to the length Lg^ or Lgg, with rotation of the ring 60 on
the screw 50 being locked by shape co-operation between
the shoulder 58 and the side of the opening 63.
The socket 56 in the head 54 may present a cross-
section other than hexagonal, for example it may be in
the shape of a six-pointed star or it may be square, as
long as it enables the screw 50 to be driven in rotation
about the axis Xjg.
As shown in Figure 1, the invention may also be used
for using two fastener devices 40 in accordance with the
invention to fasten plates 24 on the eccentric 4, each
plate forming a tooth 26 that is to co-operate with a
moving arm 28 that is itself hinged on the connecting rod
about an axis Xjg. A cap 30 retains the arm 28 on the
connecting rod 6, with the ability to pivot about said
axis. The cap 30 is mounted on the connecting rod by
means of two fastener devices 40 in accordance with the
invention. Setbacks analogous to the setback 202 are
provided in the parts 24 and 30.
The invention is not limited to the embodiments
described above and other variants may be devised by the
person skilled in the art. For example, the ring 60 may
have only one elasti,cally-deformable tab of the same type
as the tabs 64 or 66, or it may have more than two
elastically-deformable tabs. As a variant to the
chamfers 646 and 666 provided on the tabs 64 and 66,
chamfers having the same function may be provided on the
tops of the serrations 208.
gLAIM3 ^
1. A fastener device (40) for assembling together at
least two component parts (4, 20, 22) of a shed-forming
machine (2), the device comprising a screw (50) having a
threaded shank (52) and a head (54) having at least one
pair of two adjacent sides (5443-5446) forming a non-flat
angle (a^^, aj) between them, the device being
characterized in that:
• the head (54) is provided with a socket (56) for
receiving a tool for driving the screw in rotation; and
• a lock ring (60) is mounted around the screw (50)
and comprises an annular portion (62) bearing against a
face (546) of the head that is facing towards the shank
(52), together with at least one tab (64, 66) having a
first portion (648, 668) facing a first side (5444, 5445)
of a pair of sides (5443-5446) in a radial direction
relative to a central axis (X^q) of the screw, and having
a second portion (649, 669) facing the second side (5443,
5446) of the pair of sides in a radial direction relative
to the central axis (Xsq) of the screw, said second
portion (649, 669) of the tab (64, 66) being suitable for
moving towards (Fq) or away from the second side (5443,
5446) of the pair of sides by elastic deformation of the
tab.
2. A device according to claim 1, characterized in that
the axial height (Hg^, Hgg) of the tab measured parallel to
the central axis (Xjq) of the screw (50) has a value that
is greater than 50%, preferably greater than 70%, of the
value of the axial height (H54) of the head (54) measured
parallel to the central axis of the screw.
3. A device according to any preceding claim,
characterized in that the head (54) is provided with at
least two pairs of two adjacent sides (5443-5446) forming
non-flat angles (a^, aj) between them, and in that the
lock ring (60) is provided with at least two elastically-
This fastener device (40) for assembling together at
least two component parts (4, 20, 22) of a shed- forming
machine (2), comprises a screw (SO) having a threaded
shank (52) and a head (54) having at least one pair of
two adjacent sides (5443-5446) forming a non-flat angle
between them. The head (54) of the screw (50) is provided
with a socket (56) fcr receiving a tool for driving the-
screw in rotation. A lock ring (60) is mounted around the-
screw (50) and comprises an annular portion (62) bearing
against a face (546) of the head that is facing towards
the shank (52), together with at least, one tab 64, 66
having a first portion (648, 668) facing a first side
(5444, 5445) of a pair of sides (5443-5446) in a radial
direction relative to a central axis (X) of the screw
(50). A second portion of each tab is disposed radially
facing the second side (5443, b446) of the pair of sides
and is suitable for moving towards (F) or away or from the
second side (5443, 5446) of the pair of sides by of classic
deformation of the tab.
