Halex 3/4 in. Rigid Conduit Locknuts (4-Pack) 26197 - The Home Depot
Ringlock Fittings - Fresno Valves & Castings
Long Life with Stainless Steel Lock Ring Plastic Pipe Fittings Peek Three-Piece Fitting - China Peek Fittings, Plastic Pipe Fittings | Made-in-China.com
Hydraulic Fittings and Flanges | Power & Motion
Male NPT (with locking ring): Campbell Fittings
Gheen - Ring Lock Fittings by Gheen Irrigation Works