These are definitely a rare find. Ever wonder what Mark Tilden used to build his original BEAM devices out of? These things! (His original Photovore, T.H.A.B. jumper, and SunSpinner)!
These are high-precision tape transport mechanisms with 2 motors - one large pancake motor, and one worm-reduction gearmotor!
They also have quite a variety of belts & screws, a beautiful brass pulley wheel, rubber capstan pinch roller, a fine spring (what the original "omni-touch" tactile sensors were built with), and a fine coil (pancake motor encoder output).