The Model 500FA has a 3/8" center post 7-1/2" long, mounted on a rigidly-locking ball
joint, plus a fine adjustment on the center post. It includes a base measuring 1-7/8" x 1-7/8" x 1-5/8" with
three ground surfaces for sure gripping in any direction, plus a V-slot for round surfaces and an on-off push
button release. The 1/4" cross bar is 7" long, and had an adaptor for AGD (lug-back) indicators.
Model 500FA-222: Same as Model 500FA, but with GEM Model 222 dial indicator.
Model 500: Same as Model 500FA, less ball joint and fine adjustment.
Model 500-222: Same as model shown, but with GEM Model 222 dial indicator.