Use cam swivel bases when leads must rotate to face the trimmer. Ball bearing swivel bases feature dual rows of Delrin ball bearings that swivel freely even under high loads. Bases include stand-up springs and a U-Adaptor to accept a variety of appropriate blocks. The Little Swivel Cam Base is the standard configuration with a tall arm. It is ideal for mounting in the cockpit or for use on larger keelboats and small offshore boats that use 76 mm (3.00") plastic blocks.