SPECIAL UPGRADE PRICE. Upgrade a standard padlock to a Master Lock brand #3 padlock that is Master-Keyed (MK). The Master Lock #3 padlock is keyed-alike (KA) in groups with a "grand" master key for the various groups ordered (KD/MK). This lock features a hardened steel shackle, 4-pin cylinders and dual locking levers. Made in the USA. Must be purchased as an upgrade with a security kit order.