The unique patented design of these jib rollers makes them easy to snap on around stays and lifelines to protect your sails from chafe. When used on lifelines, Sail Savers help skirt the foot of the jib. They can also be used on the backstays of catamarans or other boats with large roached mainsails. Center hole is 3/16" and can be drilled out to 3/8" maximum. Two halves slide together and lock in place while two included safety clips snap on for added security.