3 1/8" Spiral Drill Collars Specifications 1.standard:API7-1 2.OD:79.4mm-279.4mm 3.factory directly delivery 3 1/8" ... drill collars are manufactured strictly from API Spec7-1 standard. HEXIN own the leading heat treatment equipment ... accordance to Standards of API 5DP, API7 &7-1, NS-1. RUSSIA RTN, RUSSIA GOST-R, ISO 9001, ... 18001, Arnco Hardbanding Certificates and so on. 3 1/8" Spiral Drill Collars