The Pallets
Ruby or sapphire are the only stones sufficiently hard from which the pallets should be made. The impulse and unlocking stones should be sloped off at the back, while the locking one is brought to an edge as indicated at d, Fig. 61, so that it may not strike the back of the tooth when returning to the locking position. The half of the locking pallet which is cut away is filled in by a half round brass plug cut off flush with the detent face. The unlocking and impulse pallets are carefully fitted to the slots and held in place by shellac. The edges of all the pallets should be slightly rounded and carefully polished.