RCBS Trim Pro Case Trimmers (See here for the full trim pro range) feature uniquely shaped shell holders to firmly hold rifle and pistol cases in perfect alignment with the cutter. This system allows for accurate and repeatable case trimming lengths and leaves the case mouths square to the body.

Trim Pro Shell Holders are numbered the same as standard shell holders to simplify identification and use. They're available for most popular rifle and pistol cartridges.

For size reference chart please see below. 

Also available here in a a Rifle set containing a #2, #3, #4 and a #10.