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Frictional kelly bar needn't unlock the joint of its inner and outer lining so that it is convenient and fast to lift the bar. Non-stair key, friction transmission the outside key is made by highly wear-resisting tempering steel. For layer of soft ground and mud, mud, (mud) sand, gravel
Interlocking kelly bar is of great pressure transmission and good anti-contortion performance. There are 3 rigid parts between drilling pipes to transfer greater pressure from embedding cylinder. And even at the hard geologic condition it can transfer greater pressure and drill in. Stair key, organization transmission, the outside key is made by highly wear-resisting tempering steel. For soft formations, (weak) weathered rock, hard strata construction.