New Ratech solid pinion bearing spacer.  Normally, the pinion has a crush sleeve, and as you tighten the pinion nut, the sleeve crushes so you can obtain proper pinion bearing preload.  A solid pinion bearing spacer does not crush, so it is much stronger.  Instead, you install the spacer and shims to achieve the proper bearing preload.  It takes a little more time to install, but is stronger than a crush sleeve. Fits the following:

70-81 Camaro/Firebird w/ GM 10 bolt 8 1/2" rear