Made in full accordance with API SPEC 11B, the couplings are high in quanlity and reasonable in price. API 1” Class SM Full Size Sucker Rod Coupling 1) Material: AISI 5140 2) Standard: API Spec 11B 3) Main specification: OD:2-3/16" (55.56mm) ID: 1-3/8"(34.93mm) Length: 4" (101.6mm) Weight: 1.13kg4)Other Size: 5/8"; 3/4"; 7/8"; 1-1/8"5)Smoothness: 3.1*10-3 6)Coat Thickness(in): 0.01in ~ 0.02in 7) ...