A typical blind rivet nut comprises a body that is hollow, partly with a plain bore and partly with a threaded portion. At the one end of the body is a flange or head that is of increased diameter. The threaded portion is remote from the end that has the flange, and between the flange end and the threaded portion is a plain bore that is of a substantially larger diameter than the major diameter of the threaded portion. The blind rivet nut may be open-ended, that is with the bore passing through the body, or it may be closed-end, that is with the one end closed. The external body of the blind rivet nut may be of a cylindrical tubular form, or can have other forms such as a hexagon or square shape in cross-section.

The typical blind rivet nut is designed so that it passes through one or more aligned apertures in application piece (s) so that the flange portion abuts the side of the application piece (s) nearest to the operator. On setting, the plain portion of the bore collapses outwardly to form a secondary bulge on the side of the application piece (s) remote to the operator.

Blind rivet nuts are particularly useful for providing thread reinforcement to thin sheet materials where it is impracticable to make a substantial thread form from the application material itself. Once the blind rivet nut has been secured to the application piece by upsetting the plain bore portion of the blind rivet nut, then another secondary part (an attachment part) can be secured to the nut by passing a bolt or set screw through a plain hole in the attachment part and into the threaded portion of the blind rivet nut.

For some applications the use of the blind rivet nut for securement of a secondary or attachment part is intermittent. For example a closed-end blind rivet nut

may be used for the application of a roof rack to a vehicle, where the user typically installs the rack only for the period of time needed. Blind rivet nuts ready to accept a roof rack are typically applied to the roof of vehicles during their manufacture, so that they are available to the user if and when needed. Usually the rivets are hidden from view beneath the trim of the vehicle. Often the trim is not particularly weatherproof and moisture is able to ingress beneath it. Moisture ingress may cause damage to the nut since the moisture ingress may result in a water-filled bore of the blind rivet nut.

Since these nuts are required to carry high loads, they are usually made from steel, and although these generally have protective coatings it is not advisable that water remain in the bore for long periods of time.

Moisture ingress may cause damage to the blind rivet nuts whether they are of an open-or closed-end type, and it is an object of the present invention to provide a plug, and a method of use of the plug, that can be applied to provide a temporary barrier to moisture or ingress of debris for the bore of set blind rivet nuts, and which preferably is provided with means to allow its easy removal from the blind rivet nut.

A first aspect of the invention provides a temporary closure plug for covering the bore of a set blind rivet nut, the plug comprising a hollow, generally cylindrical body portion that is closed at one end and has an annular flange extending radially outwardly at the other end of the body portion, the plug also comprising one or more flexible ribs extending radially outward from the cylindrical body portion.

A second aspect of the present invention provides a method of temporarily covering the bore of a set blind rivet nut, the nut having a flange with an outwardly facing surface, the method comprising inserting a plug according the first aspect of the invention, closed end first, into the bore in the blind rivet nut, such that the flange of the plug rests against the said outwardly facing surface of flange of the blind rivet nut and such that the cylindrical body of the plug extents into the bore of the nut.

Usually a blind rivet nut is assembled on an application piece, such as a vehicle roof, using a setting tool. Incorporated into the setting tool is a threaded mandrel onto

which the blind rivet nut is threaded. It is entered into the pre-prepared workpiece holes and by retracting the mandrel and supporting the flange of the nut on a nosepiece of the setting tool an axial load is applied to the nut in order to set it. In the setting process the portion of the nut adjacent the application piece, remote from the operator, collapses to form a radially enlarged ring on the side of the workpiece. It is into this collapsed bore that the temporary closure plug of the present invention is inserted.

According to the invention, the plug is provided with ribs or ridges which extend from the body of the cylindrical portion of the plug. These preferably extend annularly around the body of the cylindrical portion of the plug. Where two or more ribs are provided each is spaced at least 0.75 mm, preferably about lmm, from its neighbour. Where several ribs are present, they may be non uniformly or uniformly spaced apart.

The length of projection of each of the ribs is preferably in the range of 0.3 to 0.7mm, preferably about 0. 5mm.

The ribs may have rounded ends in order to facilitate easy entry into the bore of the blind rivet nut. Instead, the ends of the ribs may be flat or square shaped.

In the method according to the invention, the flexible rib (s) on the plug, and the plug body itself are preferably shaped and sized relative to the size of the bore of the nut such that the cylindrical body portion of the plug fits easily into the bore of the nut, but the rib (s) are deflected as the plug is inserted into the bore of the nut, so that the plug is an interference fit with the bore of the nut. The annular flange of the plug is preferably arranged to fit against the said outwardly facing surface of the flange of the blind rivet nut, and hence the bore of the nut is sealed against moisture and debris ingress.

As explained above, in the setting process of the blind rivet nut, a setting load is applied to the nut causing a portion of the nut adjacent the application piece, remote from the operator, to collapse to form a radially enlarged ring on the side of the

workpiece remote from the operator. Thus generally the bore of the set nut comprises a first generally hollow tubular portion extending from the flange of the nut through the application piece (s) and a second generally hollow tubular portion of larger internal cross-sectional area (i. e. the radially enlarged ring) extending from the first tubular portion in a direction away from the said flange of the nut. Where the plug is provided with two or more annular ribs extending around the body of the plug, some or all of the ribs may be contained within, and remain deflected by the internal bore of the first generally hollow tubular portion of the bore of the nut. Alternatively the length of the body of the plug and the distance along the length of the body of the plug from which the ribs project may be sufficiently long such that one or more annular ribs is first deflected as the rib is pushed through the first generally hollow tubular portion of the bore of the nut, and then enters the larger radially enlarged portion of the nut in the second generally hollow tubular portion of the nut where the ribs adjacent to the second hollow portion return to their original shape as more room is available.

The closure plug according to the present invention may be made from any suitable material. Preferably it comprises a polymeric material, for example polyethylene or polypropylene, or any other suitable material that will provide flexibility to the ribs of the plug.

The internal bore of the cylindrical body portion of the closure plug is preferably screw threaded along at least part of its length. More preferably it is screw threaded along most or all of its length. The reason for this preferred feature is to facilitate removal of the temporary plug when desired. Therefore a preferred method according to the invention comprises not only the step of temporarily covering the bore of the set blind rivet nut, but also the step of removing the temporary cover. In this preferred method the removal step is effected by (i) screwing an elongate member having an external screw thread into the screw threaded body portion of the plug so that the screw threads of the elongate member and the plug engage and the plug is secured to the elongate member; and (ii) withdrawing the elongate member, and with it the plug that is secured thereto. The elongate member may be the bolt that secures a secondary attachment piece as described in more detail below.

Once the temporary plug has been removed, an especially preferred method according to the invention also includes the additional step of securing a secondary part to the blind rivet nut. This is preferably effected by screwing an externally threaded member into a screw threaded portion of the bore of the nut to secure the secondary part to the nut. In a most preferred method, the externally threaded member that is screwed into the screw threaded portion of the bore of the nut to secure the secondary part to the nut is the same part as the elongate member having an external screw thread that is screwed into the body portion of the plug so that the plug is secured to the elongate member to allow removal of the plug. Thus in practice, rather than have to search for the correct threaded bolt or set screw in order to remove the temporary plug from its covering position in the nut, the bolt or set screw that is going to be used to secure the secondary part to the nut can be used to extract the sealing plug from the nut. This reduces inventory, and is of great practical help to the operator.

The plug and methods according to the present invention may be used with blind rivet nuts that are of both the closed end and open end variety. They are particularly useful in closed end type nuts since it is in these that the bore of the nut may fill up with water and consequently be most exposed to damage.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein: Figures 1A and 1B are longitudinal sectional views showing sequential steps in setting a blind rivet nut into an application piece; Figure 2 is a side view, partly in section, showing a temporary closure plug according to the invention, suitable for temporarily covering the bore in the set blind rivet nut of Figure 1B ; Figure 3 is a side, cut away, perspective view of the plug of Figure 2 installed in the bore of the set blind rivet nut of Figure 1B ;

Figure 4 is a side, cut away, perspective view of the same plug of Figure 2 installed in the bore of a blind rivet nut that is the same nut as that shown in Figure 1B and Figure 4, but is set in a thinner application piece; Figure 5 is a side sectional view of the embodiment of Figure 3, showing the use of a screw threaded bolt or set screw to remove the temporarily installed plug of Figure 4; and Figure 6 is a side sectional view showing securement of a secondary part to the first application piece, using the threaded bolt or set screw of Figure 5 once the plug has been removed.

Referring to the drawings, Figures 1A and 1B show setting of a typical closed end blind rivet nut 2 into a single application piece 4 such as the roof of a vehicle. The nut is shown prior to setting in Figure 1A and after setting in Figure 1B. Prior to setting the nut has a flanged end 6, a first cylindrical portion 8 that is relatively thin walled extending from the flange, a second thicker walled generally cylindrical portion 10 that extends from the first portion, and a closed end 11. The thinner walled portion 8 has a smooth inner bore, and the thicker walled portion has a screw threaded bore 12.

In order to install the nut a setting tool is provided comprising a threaded mandrel 14 having a threaded portion 16. The nut 2 is threaded onto the mandrel 14 so that a nosepiece of the tool (not shown) abuts the flange 6 of the nut, and then the nut and mandrel are inserted into an aperture in the application piece 4 so that flange 6 of the nut is on the operator side. Setting is effected in the usual way by holding the nut flange 6 against the surface of the application piece 4 and simultaneously pulling the mandrel 14 towards the operator in the direction indicated by arrow P in Figure 1A.

This causes the thinner, smooth walled portion of the nut 8 to collapse to form a radially enlarged ring 21 (see Figure 1B) on the side of the application piece that is remote from the operator, thereby fixing the nut in the application piece 4. The mandrel 14 is removed from the body of the nut by unscrewing the mandrel from the thread 12 of the nut. The finished set nut is shown in Figure 1B. It has a bore extending therethrough, and an internally threaded section 12 ready for receipt of a bolt or set screw or the like to secure a secondary part at some later date. However

having a closed end 11 it is also liable to water build up with consequent damage. It is therefore this bore that is to be temporarily closed.

Figure 2 shows a plug according to the invention, partly in section, that can be used to close the bore of the set nut of Figure 1B. It comprises a hollow, generally cylindrical body portion 24 that is closed at one end 26. It has an annular flange 28 extending radially outward at the other end of the body portion 24.. It also comprises a set of annular ribs 30 each extending circumferentially around the body of the cylindrical body portion 24 of the plug. The ribs are uniformly spaced apart a distance of 1 mm. The ribs project a distance of 0.5 mm radially outward. The plug has an internal screw thread 32 extending internally along the whole of the length of the cylindrical body portion 24 of the plug.

Figure 3 shows the plug of Figure 2 installed within the set closed end rivet nut of Figure 1B. The plug 22 is inserted into the bore of the nut, closed end 26 first. It is inserted so that the flange 28 of the plug rests against the flange 6 of the nut and such that the cylindrical body 24 of the plug 22 is inside the bore of the nut. The plug and ribs are chosen of a suitable size so that the cylindrical body portion 24 of the plug has a smaller diameter than that of the bore of the nut 2'and fits easily inside, but the radial extent of the ribs 30 is greater than the internal radius of the bore of the nut so that as the plug is inserted the ribs 30 are deflected to compensate for the difference in bore and rib diameter. The plug is an interference fit in the bore of the nut. Similarly the flange 28 of the plug is sufficiently large to cover the bore opening of the nut and hence the plug substantially prevents moisture ingress into the bore of the nut. The thickness of the application piece defines the length of the nut that extends on the operator side up to the blind side enlarged radius ring portion 21 resulting from setting of the nut (see Figure 1B). In the embodiment shown in Figure 3 the length of the plug body portion corresponds approximately to the thickness of the application piece so that all of the ribs projecting from the body lie within the smaller diameter (non radially enlarged) portion of the nut, and all are deflected by and in contact with the internal bore of the nut and contributing to the interference fit.

Figure 4 shows the same nut as used in Figure 1A and Figure 3 but fitted in an application piece 4'that is thinner. The same plug 22 is also used within the nut. In this case the length of the plug body portion 24 is longer than the thickness of the application piece 4'so that one of the annular ribs 30'projecting from the body of the plug has been initially deflected as the plug is pushed into the nut bore, but then sprung back to its pre-deflected position because it has passed into the radially enlarged section 21 of the nut bore where the diameter of the bore is larger than the radial extent of the rib 30'. Therefore in this case that rib 30'does not contribute to the interference fit.

As can be seen in Figures 3 and 4, the internal screw thread of the plug 22 has the same internal screw thread as that of the set blind rivet nut 2'.

When it is desired to secure a secondary part such as a roof rack to the first application piece, the temporary plug 22 must first be removed. To do this a bolt or set screw 34 having external screw threads 36 is screwed into and thus secured to plug 22 so that the external screw thread 36 of the bolt or set screw 34 engage the internal screw threads 32 of the plug 22. The bolt or set screw 34 is shown in the engaged position in Figure 5. Then the bolt or set screw 34 is withdrawn axially outward by the operator in the direction indicated by arrow W. This action causes the flexible ribs 30 of the plug to be dragged along the smooth inner wall 37 of the portion of the bore of the nut that is in contact with the ribs 30 of the plug, so that the bolt or set screw 34 and the plug that is secured thereto are both withdrawn. Bolt or set screw 34 and plug 22 can then be separated by simply unscrewing the parts.

Finally, as shown in Figure 6, an apertured secondary part, for example part of a roof rack 38, can be positioned over the blind rivet nut so that its aperture is aligned with the aperture in the first application piece 4, and the bolt or set screw 34 (the same part used to withdraw the plug 32 as shown in Figure 5) is inserted into the nut and screwed into engagement with the internal screw threaded portion 12 of the nut. The fact that the internal screw thread 32 of the plug 22 has the same inner thread diameter as the internal screw thread 12 of the set blind rivet nut 2'means that the same bolt or

set screw 34 can be used both to withdraw the plug 22 and to secure the roof rack or other secondary part. This both reduces inventory and saves the operator having to search for a correct withdrawal tool. The shank of the bolt or set screw 34 must, as shown, be sufficiently long to allow it to reach the remote screw threaded portion of the nut, and to provide it with sufficient thread engagement to withstand the applied load.

If the secondary part 38 is later to be removed (e. g. in the case of an intermittent use roof rack) then the bolt or set screw 34 is withdrawn, part 38 removed, and protective plug 22 re-inserted.