... MANUFACTURER API 11B STANDARD EXCELLENT QUALITY&REASONABLE PRICE ROCK DRILL STEEL ROD, SUCKER ROD COUPLINGCOMPANY BRIEFYantai Yunsheng Petroleum Machine Accessories Co., Ltd, ... in 1997, is a professional manufacturer of API 11B sucker rod couplings, including Spray Metal coupling, class T coupling, ... reducing the friction.PRODUCT PICTURES FOR YOUR REFERENCE rock drill steel rod, SUCKER ROD COUPLING