1. For tube casings and couplings 2. Multi-tooth thread, 8API Round 3. Twin-lock 4.Good qualit and ... years. SMT carbide API threading inserts are in multi-tooth and single-tooth, round and buttress threads, 3,4,5,8,10 ... contact us by phone and e-mail. Twin-lock Multi-tooth Carbide API Inserts for couplings