I've always used 1/4" at the heel and 3/8" at the toe. It fits me and a few others well. I start the cast off from the end of the wrist on top the end of the trigger bar, if there is one, on the bottom. Sometimes the trigger guard has to be bent to fit. The thing to remember is that the tang and trigger bar have to align with the bore or things can get cattywampus fast.