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Most JE shelf pistons include double spiro locks as standard equipment. These locks are installed by spreading the lock between 1/8" and 1/4" and rotating the lock into the groove in the piston pin boss. Wire locks are installed in much the same manner but require chamfered wrist pins. Wire locks tend to spread side loads over more of the piston pin boss area and are considered to be a stronger method of holding the pin in place. Hook wire locks have a built in hook at the end gap. The purpose for this style of wire lock is to prevent rotation within the lock groove itself. Tru arc locks fall between these two and can be used with the stock sharp edge wrist pins. The advantage of tru-arc locks is ease of installation and they can be re-used unlike spiro locks, however they are not recommended for medium to high horsepower applications.