I have solved the mystery of the pinlock and Eclip descriptions in the Chevs of the 40s catalog. When they describe the O.D. , this is the oustside diameter of the original pinlock clips. When the description describes the O. D. of the Eclip, this is the outside diameter of the original pinlock that the Eclip replaces. Thus for the large pins on the 51 1 Ton, the proper O.D. is 1 3/16". Since these parts are hard to come by, I thought that this explanation would be worth mentioning.