What is an acceptable gap between the mount plate and the quick tach?
The wrench in the photograph is a 3/4 inch craftsman and there is extra room above it. So, almost 1/2 inch gap. The photograph is looking up into the slot where the pin would be when the two components are mounted.
View attachment 580683
Right, the reason it is not touching is because it is in the wrong place. It is too close to the top angle. The latch plate should fit down flat where the wrench is, but it is hitting the angle that is in the wrong place:------------------------------------------------------------
The weld in your pic is on the bottom of the plate and don't even appear to be touching in the pic with the wrench.