Aerotight M20 A2 Grade Stainless Steel Self-Locking Nut Thread Size (Nom) - M20 Pitch - 2.5 mm A/F Max- 30.0 mm N-Dia Max - 29.47 mm H Max - 22.35 mm F Min - 15.62 mm Aerotight self locking nuts are: All metal Stiff nut with no inserts Can be re-used Will stay in position whether tightened down or not No special tools required When assembled on the screw, 2 full threads should protrude through the nut A2 stainless steel has good resistance to corrosion except in severe industrial and Marine Condition. Use A4 in a marine environment.