Bought some used tools. What the heck is this for? Couldn't find it on the Proto web site It's a Proto 4515 to be used with a 1/2" rachet. All measurements are approximate. It's 3 1/2" long.The face has a 3/4" round hole and through the side there is a offset 3/4" hole. Set 1" from the face there is a centered 1/4" hole as well. It is stamped "Made in the U.S.A."