Patent Description:
Barrel nuts are used in a number of applications, particularly in the aerospace industry, where it is either undesirable for the tail end of a fastener to protrude through the surface of a component or where there are no accessible opposing surfaces between which a nut may be tightened onto the fastener.

Assembly generally involves placing the barrel nut into the bore of a component, such that a threaded through-hole of the barrel nut aligns with a fastener passing through the component. As rotation of the barrel nut relative to the longitudinal axis of the fastener is restricted by the fastener, the barrel nut is able to tighten onto the fastener.

However, whilst rotation of the barrel nut relative to the longitudinal axis of the fastener is restricted when attached to a fastener, when the barrel nut is not attached to a fastener the barrel nut is free to rotate relative to its longitudinal axis and to translate along the bore into which it is placed. This makes alignment of the barrel nut with the fastener difficult and time-consuming.

In addition, it is an ambition in the aerospace industry to improve build and assembly times for aircraft. One way to do this is to provide certain systems and sub-assemblies as selfcontained modular units which can be more quickly and easily assembled to the major assembly. Barrel nuts are key enablers to allow for this modular assembly style. However, when a barrel nut is installed into a sub-assembly module which is then, for example, transported to another location for assembly to the major assembly, rotation and translation of the barrel nut can occur, leading to a need to re-align the barrel nut, or even loss of the barrel nut completely.

This uncertainty of barrel nut orientation also means that use of barrel nuts in automated assembly lines and automated assembly processed is unsuitable. For instance, if a barrel nut were to change orientation in an automated assembly process prior to a fastener or bolt being inserted therein, then it could cause significant delays while the line stops to allow for human intervention to re-orientate the barrel nut for the automated assembly process to continue.

<CIT> describes a barrel nut retainer which can be used to retain a barrel nut inside a bore, and which comprises a feature that allows the barrel nut to be easily repositioned to a desired rotational position.

<CIT> discloses a barrel nut retention apparatus for retaining a barrel nut within a cylindrical bore in a panel comprising a barrel nut and retaining means.

<CIT> discloses a barrel nut with spring retainer member.

According to a first aspect of the invention, there is provided a barrel nut assembly comprising: a barrel nut; and a barrel nut positioning frame for maintaining a barrel nut in a desired position in a bore of a component, the frame comprising: a frame body configured to receive a barrel nut therein, the frame body being adapted to fit, together with a received barrel nut, within a bore; and a bore engagement element configured to engage with a positioning feature in the bore so as to restrict movement of the frame within the bore, wherein the frame body comprises a spine extending longitudinally along a length of the barrel nut, and at least one circumferential prong extending at least partially around an outside circumference of the barrel nut.

A further aspect of the invention provides an assembly, comprising: a component with a first bore and a second bore perpendicular to the first bore, the first bore having a positioning feature therein; the barrel nut assembly insertable into the first bore; and a fastener insertable into the second bore to threadingly engage with a threaded through-hole in the barrel nut.

Also disclosed but not claimed is a method for assembling an aircraft assembly, comprising: providing a first component having a first bore and a second bore perpendicular to the first bore and intercepting the first bore, the first bore having a positioning feature formed therein; selecting a barrel nut positioning frame according to a previous aspect of the invention, wherein the barrel nut positioning frame is selected based on the positioning feature formed in the first bore; inserting a barrel nut into the barrel nut positioning frame to form a barrel nut assembly according to another previous aspect of the invention; and inserting the barrel nut assembly into the first bore such that the bore engagement element of the frame engages with the positioning feature in the first bore.

With such an arrangement it is possible to use the barrel nut positioning frame to ensure that a barrel nut is held in position within a bore. As such, when a fastener is to be fixed into the barrel nut during an assembly process, it is not necessary to check the position of the barrel nut and re-orientate it if needed before inserting the fastener. This allows for a much quicker, simpler and more efficient assembly process. In addition, it allows for the use of barrel nuts in an automated assembly process. Previously, barrel nuts have not been deemed suitable for automated assembly processes due to the uncertainty of barrel nut orientation.

Optionally, the bore engagement element may be configured to engage with a positioning feature in the bore so as to restrict movement of the frame within the bore for at least <NUM> degrees of freedom.

Optionally, the bore engagement element may be configured to engage with a positioning feature in the bore so as to substantially prevent rotation of the frame around a longitudinal axis of a barrel nut received therein.

Optionally, the bore engagement element may be configured to engage with a positioning feature in the bore so as to substantially prevent translation of the frame within the bore along a longitudinal axis of a barrel nut received therein.

Optionally, the frame body may comprise a barrel nut engagement element configured to engage with a feature in the barrel nut so as to restrict movement of the barrel nut within the frame.

Optionally, the barrel nut engagement element may be an inwardly-directing protrusion, and the feature in the barrel nut may be a recess formed in the outer surface of the barrel nut, and the inward-directing protrusion is received into the recess.

Optionally, the bore engagement element may comprise an outwardly directing protrusion.

Optionally, the outwardly-directing protrusion may be a convex formation formed in the frame, the convex formation extending radially outwards.

Optionally, the outwardly-directing protrusion may be a spring-biased hook that is biased radially outwards.

Optionally, the positioning feature in the bore may be a machined recess in the inner wall of the bore, and the outwardly directing protrusion may be configured to be received in the machined recess.

Optionally, the frame may comprise a leaf spring element configured to provide a biasing force against an inner wall of the bore.

Optionally, the outwardly directing protrusion of the bore engagement element of the frame may engage with the positioning feature in the first bore, so as to restrict movement of the barrel nut assembly within the bore.

Optionally, the assembly may be an aircraft assembly and the component may be an aircraft component, or the assembly may be an automotive assembly and the component may be an automotive component.

<FIG> shows an aircraft <NUM> with port and starboard fixed wings <NUM>, <NUM>, and a fuselage <NUM> with a nose <NUM> and a tail <NUM>. The aircraft <NUM> is a typical jet passenger transonic transport aircraft but the invention is applicable to a wide variety of fixed wing aircraft types, including commercial, military, passenger, cargo, jet, propeller, general aviation, etc. with any number of engines <NUM> attached to the wings or fuselage.

Each wing <NUM>, <NUM> has a cantilevered structure with a length extending in a span-wise direction from a wing root <NUM> to a wing tip <NUM>, the wing root <NUM> being joined to the fuselage <NUM>. The wings <NUM>, <NUM> are similar in construction so only the port wing <NUM> will be described in detail with reference to the following Figures.

In the following description, the term "front" refers to components towards a leading edge <NUM> of the wing, and the term "rear" refers to components towards a trailing edge <NUM> of the wing. The terms "forward" and "rearward" should be construed accordingly. The position of features may be construed relative to other features, for example a forward component may be disposed on a forward side of another component, but towards the rear of the vehicle. Similarly, the terms "upper" and "lower" refer to the position of features relative to other features and in accordance with a normal orientation of the aircraft <NUM>.

<FIG> shows a schematic view of a wing box <NUM> of the port wing <NUM> of an aircraft <NUM>. The wing box <NUM> is a support structure arranged to support a significant proportion of the loads on the wing <NUM>. The wing box <NUM> has a forward spar <NUM>, an aft spar <NUM>, an upper cover <NUM>, and a lower cover <NUM> each extending substantially the entire length of the wing <NUM>. The upper cover <NUM> and lower cover <NUM> have outer aerodynamic surfaces. The wing <NUM> also includes a leading edge structure (not shown) and a trailing edge structure (not shown) that are aerodynamically shaped to combine with the wing box <NUM> to form an aerofoil shaped body.

The forward spar <NUM> and aft spar <NUM> are 'C-shaped', each spar <NUM>, <NUM> including inward facing flanges 13a, 13b, 14a, 14b that provide attachment portions for attaching the spars <NUM>, <NUM> to the covers <NUM>, <NUM>. 'Inward facing' refers to the flanges extending towards the centre of the wing box <NUM>, such that the flanges 13a, 13b of the forward spar <NUM> extend aft towards a trailing edge <NUM> of the wing <NUM> and the flanges 14a, 14b of the aft spar <NUM> extend forward towards a leading edge <NUM> of the wing <NUM>.

In an alternative embodiment not shown in the figures, the forward spar <NUM> and aft spar <NUM> may include outward facing flanges that provide attachment portions for attaching the spars <NUM>, <NUM> to the covers <NUM>, <NUM>. Outward facing' refers to the flanges extending away from the centre of the wing box <NUM>, such that the flanges of the forward spar <NUM> extend forwards towards a leading edge <NUM> of the wing <NUM> and the flanges of the aft spar <NUM> extend aft towards a trailing edge <NUM> of the wing <NUM>.

<FIG> shows a schematic of an aft section of the wing box <NUM>, in which an attachment bracket <NUM> is connected to the rear spar <NUM>. The attachment bracket enables preassembled modules to be fixed to the rear spar <NUM> during assembly of the wing <NUM>. This modular assembly allows for a much quicker and simpler assembly than traditional methods.

<FIG> shows a sub-assembly module <NUM>, e.g. an aircraft wing trailing edge system module, coupled to the attachment bracket <NUM>. The connection between the sub-assembly module <NUM> and the attachment bracket <NUM> is achieved via a captive nut solution. A fastener <NUM> in the form of a bolt extends through the sub-assembly module <NUM> and into a barrel nut (not shown) held captive within a bore <NUM> of the attachment bracket <NUM>.

A barrel nut and fastener combination is required due to the limited access to the upper rearward portion of the wing box <NUM>, and in particular the lack of opposing surfaces upon which to tighten a nut onto the fastener <NUM>.

The connection is formed by inserting the barrel nut into the bore <NUM> of the attachment bracket <NUM>, inserting the fastener <NUM> through a bore in the sub-assembly module <NUM> and attachment bracket <NUM>, wherein the fastener bore connects with and is perpendicular to the bore <NUM> into which the barrel nut is inserted. In this manner, the fastener <NUM> can be inserted into a threaded through-hole of the barrel nut. As rotation of the barrel nut relative to the longitudinal axis of the fastener is restricted by the fastener, when the fastener is inserted through the barrel nut, the barrel nut is able to tighten onto the fastener.

However, whilst rotation of the barrel nut relative to the longitudinal axis of the fastener is restricted when attached to a fastener, when the barrel nut is not attached to a fastener, a standard barrel nut would be free to rotate about its own longitudinal axis and to translate along the bore into which it is placed. This would make alignment of the barrel nut with the fastener difficult and time-consuming. The restricted access at the aft portion of the wing box <NUM> shown in <FIG> also means that manipulation of the barrel nut within the bore is made even more challenging.

There is also a risk that a standard barrel nut would slide out of the bore and be lost, which is a particular concern with aircraft assemblies.

To address these problems, a barrel nut assembly can be used which comprises a barrel nut which is located inside a barrel nut positioning frame. In addition, a positioning feature is provided in the bore <NUM>. The barrel nut assembly will be described in more detail below, but the frame enables the barrel nut to maintain a desired position within the bore <NUM> by engaging with the positioning feature in the bore <NUM>.

A perspective view of a schematic representation of the attachment bracket <NUM> is shown in <FIG>. The attachment bracket <NUM> has a first bore, bore <NUM> which extends through the attachment bracket <NUM>. The attachment bracket <NUM> also has a second bore <NUM> and a third bore <NUM>. The second and third bores <NUM>, <NUM> extend through the body of the attachment bracket perpendicular to the first bore <NUM>, and intercept the first bore <NUM>.

Two barrel nut assemblies <NUM>, <NUM> are inserted into the bore <NUM>, barrel nut assembly <NUM> being inserted through bore aperture <NUM>, and barrel nut assembly <NUM> being inserted through bore aperture <NUM> as indicated by arrows A and B. Barrel nut assembly <NUM> is inserted into the bore <NUM> until its threaded through-hole <NUM> is aligned with the second bore <NUM> in the attachment bracket. Similarly, barrel nut assembly <NUM> is inserted into the bore <NUM> until its threaded through-hole <NUM> is aligned with the third bore <NUM> in the attachment bracket.

When each barrel nut assembly <NUM>, <NUM> is in place, a bore engagement element (not shown) of each barrel nut assembly engages with a positioning feature (not shown) in the first bore <NUM>. This restricts movement of each barrel nut assembly <NUM>, <NUM> within the bore <NUM>, and ensures that the threaded through-holes <NUM>, <NUM> remain aligned with the second and third bores <NUM>, <NUM>.

Fasteners <NUM> can then be inserted through the second and third bores <NUM>, <NUM>, as indicated by dotted-line arrows C and D, to threadingly engage with the threaded through-holes <NUM>, <NUM> in the barrel nut assemblies <NUM>, <NUM>.

In <FIG> the bore <NUM> extends through the entire body of the attachment bracket <NUM> in the embodiment shown. However, it will be appreciated that in alternative embodiments an attachment bracket may comprise a number of individual bores which do not extend fully through the body of the bracket.

<FIG> show a first embodiment of a barrel nut assembly <NUM>. <FIG> shows the barrel nut assembly of <FIG> rotated <NUM>° around the x-axis shown in the Cartesian coordinate system x,y,z axes.

The relative orientations of the barrel nut assemblies described herein can be more easily understood using the Cartesian coordinate system x,y,z axes which are provided where necessary in the Figures for reference purposes only.

The barrel nut assembly <NUM> comprises a barrel nut <NUM> and a barrel nut positioning frame <NUM>. The barrel nut <NUM> is a fairly typical barrel nut comprising a generally cylindrical body <NUM> and a threaded through hole <NUM>. The threads of the threaded through-hole <NUM> are not shown in the Figures for the sake of clarity.

The barrel nut positioning frame <NUM> comprises a frame body which is configured to receive the barrel nut <NUM> therein. The frame body comprises a spine <NUM> extending longitudinally along the length of the barrel nut <NUM>. The frame body also comprises two pairs of circumferential prongs <NUM>, <NUM> extending from the spine <NUM>. The circumferential prongs extend around the outside circumference of the barrel nut <NUM> to enclose it within the positioning frame <NUM>.

The positioning frame <NUM> also comprises a barrel nut engagement element in the form of inwardly-directing protrusions <NUM> located at the end of prongs <NUM>. The inwardly-directing protrusions are configured to engage with small recesses <NUM> formed in the barrel nut <NUM>, such that movement of the barrel nut <NUM> within the positioning frame <NUM> is restricted.

The spine <NUM> of the positioning frame <NUM> has an outwardly convex profile, such that the spine <NUM> forms an outwardly-directing protrusion. This enables the spine <NUM> to engage with a positioning feature formed in a bore of a component, as will be described below in reference to <FIG>.

<FIG> shows a representation of a cross section through the barrel nut assembly <NUM> in position inside a component, such as the attachment bracket <NUM> of <FIG>. The same reference numbers for equivalent features shown in <FIG> will therefore be used. The barrel nut assembly <NUM> is inside the bore <NUM> of the attachment bracket <NUM>. The bore <NUM> is provided with a positioning feature in the form of a recess 24A formed in the wall of the bore <NUM> and which extends along the length of the bore <NUM>. The barrel nut assembly <NUM> is inserted into the bore <NUM> such that the outwardly-directing protrusion of the spine <NUM> is received inside the recess 24A. As such, the outwardly-directing protrusion of the spine <NUM> engages with the recess 24A in order to prevent the barrel nut assembly <NUM> from rotating about its longitudinal axis. This ensures that the threaded through-hole <NUM> of the barrel nut <NUM> remains aligned with the second bore <NUM> of the attachment bracket <NUM>.

As such, when the barrel nut assembly <NUM> is assembled into the bore <NUM>, movement of the positioning frame <NUM>, and therefore the entire barrel nut assembly <NUM>, is restricted in five of its six degrees of freedom. The remaining degree of freedom left for the barrel nut assembly is that it is able to translate through the bore along the longitudinal axis (x-axis) of the barrel nut.

<FIG> show a second embodiment of a barrel nut assembly <NUM>. The barrel nut assembly <NUM> comprises the same barrel nut <NUM> described in the embodiment of <FIG> and a barrel nut positioning frame <NUM>.

The barrel nut positioning frame <NUM> comprises a frame body which is configured to receive the barrel nut <NUM> therein. The frame body comprises a spine (hidden from view underneath the barrel nut <NUM>) extending longitudinally along the length of the barrel nut <NUM>. The frame body also comprises two pairs of circumferential prongs <NUM>, <NUM> extending from the spine. The circumferential prongs extend partially around the outside circumference of the barrel nut <NUM> to help retain it within the positioning frame <NUM>.

The positioning frame <NUM> further comprises a head end <NUM> and a tail end <NUM>. Unlike the barrel nut assembly of <FIG>, the barrel nut assembly of <FIG> does not comprise an engagement between inwardly-directing protrusions of the frame and recessed in the barrel nut <NUM>. Instead, a frictional engagement between the frame <NUM> and the barrel nut <NUM> is sufficient to restrict movement of the barrel nut <NUM> within the positioning frame <NUM> and maintain correct orientation.

The positioning frame <NUM> further comprises a spring-biased hook <NUM> attached to the head end <NUM>. The spring-biased hook <NUM> forms an outwardly-directing protrusion which can engage with a positioning feature formed in a bore of a component, as will be described below in reference to <FIG>.

<FIG> shows a representation of a cross section through the barrel nut assembly <NUM> during assembly of the barrel nut assembly itself. The frame <NUM> is formed of an elastic material such as metal or a plastic material. To insert the barrel nut <NUM> into the frame <NUM>, the frame is simply elastically deformed allowing the barrel nut <NUM> to be inserted into it. In particular, <FIG> shows the tail end <NUM> of the frame <NUM> being deformed.

<FIG> shows a cross section through a bore <NUM> in a component <NUM>. The bore <NUM> is the bore into which the barrel nut assembly is to be inserted. The bore <NUM> is the bore through which a fastener or bolt can be inserted in order to fasten to a barrel nut. The bore <NUM> comprises a positioning feature in the forms of a recess <NUM> in the inner wall of the bore <NUM>. This recess <NUM> can be machined easily by extending part of the opening of the second bore <NUM> to the point that the intersection with the first bore <NUM> is reached.

<FIG> shows the component <NUM> during insertion of the barrel nut assembly <NUM> into the bore <NUM>. Movement of the barrel nut assembly <NUM> into the bore <NUM> is indicated by arrow E. The spring-biased hook <NUM> is biased into a flattened configuration to allow the barrel nut assembly <NUM> to fin into the bore <NUM>. The bore <NUM> does not extend as a through-hole through the whole component <NUM>. Instead, the depth of the bore is controlled such that when the barrel nut assembly <NUM> abuts against the end <NUM> of the bore <NUM>, the threaded through-hole <NUM> of the barrel nut <NUM> is aligned with the second bore <NUM> in the component <NUM>.

<FIG> shows the barrel nut assembly <NUM> abutting against the end <NUM> of the bore <NUM>. At this position, the spring-biased hook <NUM> has reached the recess <NUM> and therefore the biasing force in the hook <NUM> has caused it to revert to the protruding configuration such that it protrudes into, and engages with the recess <NUM>. In this position, if the barrel nut assembly <NUM> attempts to move, for example by translation along or rotation around the longitudinal axis (x-axis), the spring-biased hook <NUM> will come into contact with the sides of the recess <NUM>, and prevent significant movement. The engagement of the spring-biased hook <NUM> in the recess <NUM> therefore restricts movement of the positioning frame <NUM>, and therefore the entire barrel nut assembly <NUM>, in all six degrees of freedom of the barrel nut assembly <NUM>.

The embodiment shown in <FIG> requires fairly strict control over the size of the positioning frame <NUM> and also over the depth of the bore <NUM>. An alternative embodiment is shown in <FIG> which allows for a larger error margin in the size of the bore, and also in the size of the positioning frame.

<FIG> show a third embodiment of a barrel nut assembly <NUM>. The barrel nut assembly <NUM> comprises the same barrel nut <NUM> described in the previous embodiments and a barrel nut positioning frame <NUM>.

The barrel nut positioning frame <NUM> comprises a frame body which is configured to receive the barrel nut <NUM> therein. The frame body comprises a spine <NUM> extending longitudinally along the length of the barrel nut <NUM>. The spine <NUM> of this embodiment is longer then the length of the barrel nut <NUM> such that the frame extends beyond the length of the barrel nut <NUM>. The frame body also comprises two pairs of circumferential prongs <NUM>, <NUM> extending from the spine. The circumferential prongs extend partially around the outside circumference of the barrel nut <NUM> to help retain it within the positioning frame <NUM>.

The positioning frame <NUM> further comprises a head end <NUM> and a tail end <NUM>. As with the embodiment described in <FIG>, a frictional engagement between the frame <NUM> and the barrel nut <NUM> is sufficient to restrict movement of the barrel nut <NUM> within the positioning frame <NUM> and maintain correct orientation.

The positioning frame <NUM> comprises a spring-biased hook <NUM> attached to the head end <NUM>. The spring-biased hook <NUM> forms an outwardly-directing protrusion which can engage with a positioning feature formed in a bore of a component.

The positioning frame <NUM> further comprises a first leaf spring element <NUM> at the head end <NUM>. The first leaf spring element <NUM> extends inwards from the head end <NUM> towards the barrel nut <NUM>. The first leaf spring element <NUM> therefore provides a biasing force against the barrel nut <NUM> such that it is urged into abutment with the tail end <NUM>.

The positioning frame <NUM> further comprises a second leaf spring element <NUM> at the tail end <NUM>. The second leaf spring element <NUM> extends outwards from the tail end <NUM> towards the end face of a bore in which the barrel nut assembly <NUM> can be located. The second leaf spring element <NUM> therefore allows for a margin of error in manufacturing tolerances when a bore is formed in a component that the barrel nut <NUM> will be installed in.

<FIG> show a fourth embodiment of a barrel nut assembly <NUM>. The barrel nut assembly <NUM> comprises the same barrel nut <NUM> described in the previous embodiments and a barrel nut positioning frame <NUM>. The barrel nut positioning frame <NUM> is similar to that described in <FIG>, and only the differences shall be focussed on here, equivalent features found in previously described embodiments shall not be discussed for the sake of conciseness.

The positioning frame <NUM> does not have a tail end as found in previous embodiments. The two pairs of circumferential prongs <NUM>, <NUM> extending from the spine extend partially around the outside circumference of the barrel nut <NUM> to help retain it within the positioning frame <NUM>, and at the distal end of the prongs <NUM>, <NUM> from the spine, each of the prongs is provided with a barrel nut engagement element in the form of an inwardly-directing protrusion <NUM>. The inwardly-directing protrusions <NUM> are configured to engage with small recesses <NUM> formed in the barrel nut <NUM>, such the barrel nut <NUM> is retained within the positioning frame <NUM>, and that relative movement between the two is restricted.

<FIG> show a fifth embodiment of a barrel nut assembly <NUM>. The barrel nut assembly <NUM> comprises the same barrel nut <NUM> described in the previous embodiments and a barrel nut positioning frame <NUM>. The barrel nut positioning frame <NUM> is similar to that described in <FIG>, and only the differences shall be focussed on here, equivalent features found in previously described embodiments shall not be discussed for the sake of conciseness.

The barrel nut positioning frame <NUM> has a bar <NUM> that protrudes inwardly from the head end <NUM> towards the barrel nut <NUM>. The bar <NUM> engages with a screwdriver engagement slot 44A that is formed in one end of the barrel nut <NUM>. The barrel nut positioning frame <NUM> also has a bar <NUM> that protrudes inwardly from the tail end <NUM> towards the barrel nut <NUM>. The bar <NUM> engages with a second screwdriver engagement slot 44A that is formed in the other end of the barrel nut <NUM>. As such the barrel nut <NUM> is retained within the positioning frame <NUM>, and that relative movement between the two is restricted.

It will be clear to the skilled person that the examples described above may be adjusted in various ways, and features of some embodiments may be combined with other embodiments depending on the application and requirements.

In alternative examples, the recess <NUM> may instead be suitable for engaging with a different shaped tool, or may be a protrusion providing a surface to which a tool (or user) can grip the retainer <NUM>.

The positioning frame is described as being formed from metal or plastic. For instance the positioning frame may be formed from ABS, or from other plastics materials such as Polylactic Acid (PLA) and polycarbonate. The positioning frame may also be formed of other materials, such as stainless steel, nickel alloys, aluminium, or any other suitable metal.

In some examples, some parts and elements are described as being formed as a leaf spring, however they may instead use a compression spring component and still provide the same functionality.

Claim 1:
A barrel nut assembly (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>), comprising:
a barrel nut (<NUM>); and
a barrel nut positioning frame (<NUM>, <NUM>, <NUM>) for maintaining the barrel nut in a desired position in a bore (<NUM>, <NUM>) of a component (<NUM>), the frame comprising:
a frame body configured to receive the barrel nut therein, the frame body being adapted to fit, together with a received barrel nut, within a bore; and
a bore engagement element configured to engage with a positioning feature (24A) in the bore so as to restrict movement of the frame within the bore,
wherein the barrel nut is located in the frame body and the frame body comprises a spine (<NUM>) extending longitudinally along a length of the barrel nut, and at least one circumferential prong (<NUM>, <NUM>, <NUM>, <NUM>) extending at least partially around an outside circumference of the barrel nut.