Lincoln Industrial 5291 Grease Fittings, 1/4"-28 Taper Thread, 45-Degree Angle, Case of 10. Part Number: 5291. Q: What is the thread size of the Lincoln Industrial 5291 Grease Fittings?. A: The 5291 Grease Fittings have a 1/4"-28 taper thread, suitable for standard grease guns.
