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 216 features a second cleat for lines led vertically through the base of the swivel. It is frequently used to combine vang or backstay controls in the same swivel base that handles the mainsheet. Delrin ® is a registered trademark of E. I. du Pont de Nemours and Company or its affiliates.