API Spec 11 BOIL DRILLING STABILIZERS, SUCKER ROD COUPLING PROFESSIONAL MANUFACTURER EXCELLENT QUALITY&REASONABLE PRICE Yantai Yunsheng Petroleum Machine Accessories Co., Ltd, founded in 1997, is a professional manufacturer of API 11B sucker rod couplings, including Spray Metal coupling, class T coupling, Altra High Strength,Sub OD coupling, with various spec. of Full size, Slim Hole, grand ...