Davis Sail track stop # 2350. This is a round track stop. Large knurled nut for positive grip. Fits almost any slotted spar with round luff groove. Slug is aluminum and some spars/masts it needs to be ground or sanded down some to fit in the opening gate. This is the only size round track stop that Davis makes. The internal portion of the stop is 1/2″ diameter. These work great to keep the sail slides on the main sail in the track so they down fall out when your lower your mainsail.