The Forbes Grip Nut

Post date: 03-Oct-2013 07:01:20

This is an article from the 1903 Engineer Magazine, describing a new invention known as the Forbes Grip Nut. It was apparently quite common, and used extensively for some decades. The uses described for it are similar to those used these days by nyloc nuts and the like.

THE two illustrations herewith show the grip nut lately brought out by the Forbes Rail and Grip Nut Syndicate, of Cannon-street. It may be said that this nut in reality consists of two portions-although one of these is but a washer - since the one without the other is of no use. 

In Fig. 1 the top of the screw bolt is shown coming through the washer. The hole in the latter is tapered, the larger diameter of hole being at the top. It will be seen that this hole is considerably larger than the bolt. In this figure the nut proper is seen on the right-hand side. It is much deeper than an

ordinary nut, and its lower portion is turned off parallel and has four slots cut in it. The size of this turned-off portion is such that it just enters the hole in its washer, and, since the latter is tapered, and since the extension of the nut is slotted, a gripping action on the bolt is set up as soon as the nut enters the washer hole. Moreover, the grip gets greater as the nut is screwed further and further “ home.” 

Fig. 2 shows the nut screw right “ home.”

A number of advantages are claimed for this nut :-First, that it has three pressures, viz.: (1) Face pressure, as an ordinary nut ; (2) friction pressure between the extension of the nut and the washer; and (3) the pressure of the thread inside the extension of the nut and the thread of the bolt. It is further claimed as an advantage that it is free from springs, extra screws or any complication; that since the inside of the washer is tapered and smooth, the nut is as easy to screw off as to screw on, and can be used any number of times. No drilling or other weakening of the bolt is necessary.

It is said that the nut has been subjected to tests on marine engines, rock-drilling and stone-crushing machinery, without shaking loose, and its makers particularly recommend its use for agricultural and other machinery, marine engines, ordnance, and motor cars.