On Oct 9, 4:54 pm, "Tim W" wrote:
Curious. I see these on ebay and I don't know what they are for. Item
260167202747for example.

Your standard door hinge is a butt hinge. http://www.taunton.com/finewoodworking/pages/w00136.asp

A butt gauge is used to layout the jamb mortise for the hinge leaf.

R