... 300 people, including more than 50 professional and technical personnel, and in collaboration with a number of research ... K, D, KD, HL, HY and KH. Among them, grade C, K, D sucker rods are designed and manufactured ... according to the API Spec 11 B, grade KD, HL and ... sucker rod, having the same size and main parameter as grade D sucker rod, but their strength ...