Posted for "sqpilot@earthlink" <sqpilot@earthlink.net>:

 Hi, Scott....I measured mine with a depth micrometer and also with dial
calipers. My setback measures .385, or 3/8 of an inch plus .010.   I just
used a 3/8 spacer, and tightened the bolt and it clamped right down on my
3/8" spacer almost immediately. (Not much torque required on the bolt). Hope
this helps. Paul Conner 1989 13b turbo engine.