The Westcott style two jaw chuck accepts mortising bits with up to 16mm dia with part number MCK16

The Westcott style two jaw chuck accepts mortising bits with up to 20mm dia with part number MCK20

M20x1.5 thread is for C3-260, C3-310Q, C5-260, C5-260H and C5-310Q

M33x1.5 thread is for C3-310, C3-410Q, C3-410HD, C5-310H, C5-410H and MS3016