Bob Engelhardt writes:

Anybody have any experience with SPI stuff?

http://www.use-enco.com/CGI/INSRIT?PMAKA=319-3110

The 3/8" version has worked well for me. The first time using it I had to
indicate a test rod and rotate the mounting on the arbor to get it centered
to a repeatable thou or two when it was new, but since then no trouble.