30 is bifurcated to form two arms 42 and 44 aligned bores 46 and 48 are formed in the arms 42 and 44 adjacent these outer ends and are adapted to receive a clevis pin 50 a locking pin 60 having a stem portion 62 and an enlarged head portion 64 is slidably received in the bore 66 through the bushing 10 the end of the head portion 64 is chamfered as shown at 68 the end of the stem portion 62 is flatened as illustrated at 69 and provided with a transverse bore 70 for connection with a retracting mechanism a spring 72 surrounds the stem portion 62 and is confined between two thrust washers 74 and 76 one of which bears against the bushing 12 and the other against the head portion 64 two short metal links only one of which is shown at 80 in fig1 are fastened one on either side of the flat end 69 of stem portion 62 by a clevis pin 82 a clevis pin 84 connects the other ends of the links to one corner of a triangular member 86 another corner of the member 86 is pivotally mounted on the previously described clevis pin 50 a third hole 87 is provided in triangular member 86 adjacent the third corner thereof in operation of the device the inner member 90 of the mast 20 is raised relative to the outer member 18 until the socket 92 is adjacent the head 64 of the pin 60 at this time the pin is retracted by moving the triangular member 86 to the right as viewed in fig1 about the clevis pin 50 since the bracket 30 and the pin 60 are freely rotatable relative to the bushing 12 this movement would in.