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.