Compatible OPC drum haven't a metal gear. This gear should be remove from the original OPC drum with help a flat screwdriver and it uses in compatible OPC drum.
Also searched as:
Hewlett Packard (HP) LaserJet Pro 400 M 401,M401, LJ M401, Laser Jet M401, Laser JetM401,
ProM401, LJ ProM401, Laser Jet ProM401, Laser JetProM401,
HPLJPro400