Bosch chuck keyed 12in x 20 unf with key bosch 1608571062 these keyed chucks from bosch have a 12in x 20 unf thread fitting and are supplied with a key keyed chucks up to 13 mm 15 13 mm 12 20 bosch 1608571062 chuck keyed 15 to 13mm 12in x 20 unf forwardreversehammer