Dave: The screw you describe may have different names: tri-tip, tri-wing, tri-oval or other variations. If I am correct, they were used in the aircraft industry. I have one tip which would be too large for you're application. It reads, nash 4005D, air-tuf & has a "6" circled, indicating the size of the tip. A google search came up empty but you may find help at you're local Airport Maintenance facility. A close inspection of the screw will probably show tapered slots in the reverse direction which is normal for that type screw. All you never wanted to know about screws and NO help. Sorry! Jim M.