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 Bullseye Swivel Base with 150 Cam-Matic are simple swivel bases for main and jib sheets on very small boats or for control lines on boats of all sizes.