OFNA Racing Division Collet, Flywheel Insert: .12,.21 This is the Ofna .21/.15 engine tapered split brass corn.Features:This is installed on the crankshaft and is directly in front of the front bearing. This centers the flywheel.This can fit other engines that has a 7mm outside diameter area directly in front of the front bearing before the threaded portion of the crankshaft.