Adjustable timing gear. Works with timing cover installed. Fits 026, 049, 053 type watercooled 4-cylinder 8V engines (from '75 - 1999, including ABA). Also works in older VW/Audi 10v. Advance and retard the camshaft relative to piston position to bias peak torque to high or low rpms.
Note: Check here for cam timing advice.