Not only does the Snap-on Reverse Input Drum Seal Sizer help insure proper seal installation in popular GM transmissions, it will also save service technicians time and effort because of the efficiency of the tool. By using the Snap-on Reverse Input Drum Seal, tricky installation of reverse input drum and over stator shaft is simplified by pre-shaping the Teflon® seal with this special seal sizing tool. The Snap-on Reverse Input Drum Seal works on GM transmissions from 1982 to present such as 4L60, 4L60-E and 4L65-E automatic transmissions.