Chuck Key for use with 48-66-5185 This chuck key tightens the jaws of the 1/2" capacity chuck 48-66-5185. Key holder 48-66-4040 should be used to attach this chuck key to the cordset. Features: For use with 48-66-5185 Use with Key Holder 48-66-4040 Since its founding in 1924, Milwaukee has focused on a single vision: To produce the best heavy-duty electric power tools and accessories available to the professional user. Today, the Milwaukee name stands for the highest quality, durable and reliable professional tools money can buy.