Designation Description Page External & internal, API V-type (API SPEC 1238 API - Oil Threads 74-1994) API buttress casing, external & internal (ANSI 1239 API - Oil Threads B1.9-1973 CLASS 2) API extreme line casting, external & internal 1240 API - Oil Threads (ANSI B1.9-1973 Class 2) External & internal (API spec 5b-8-1996), regular 1241 Round DIN 405 and M-type 1182