A clamping unit for releasably holding a tubular toolholder shank has a base member with a canister sleeve mounted therein. To secure the canister sleeve within the base member and to minimize movement caused by tolerances, retention bolts are threadably mated within the base member to engage a slot within the canister, wherein the relationship between the retention bolt and the slot is such that the retention bolt is intentionally misaligned, so that when engaged with the canister slot, the retention blot resiliently deflects and provides both an axial force and a lateral force upon a canister sleeve.