1 Piece Apex Seals VS 2 Piece Apex Seals for a 13B Rotary on a RX7 (Part 1) Within your two millimeter 13b apex line up there's variations and materials corner piece design spring layouts but if you really look at it all of the manufacturers really had the same goal in mind if it's a two-piece or even a three-piece design you're looking at long term sealing the ability for the seal to slide around and move within the motor is just a great seal and the one-piece design it's just manufactured for …..