a device used to remove wrinkles and minor twists in a sail, so its luff tape/boltrope will slide smoothly into a luff groove’s sail feed opening on a mast or head foil. This allows for hoisting the sail more easily and quickly, and prevents damage to the sail. One pre-feeder type is a semi-circular ring with an opening slightly larger than luff tape. On either side of the opening are large rollers. Another type consists of a pair of smooth prongs that radiate aft, downwards, and outwards from either side of the sail feed. The purpose of each design is to accommodate the severe angles of the incoming luff tape and to redirect it towards the feeder. The roller types are also known as monkey balls or monkey nuts.