The enlarged and threaded ends of joints of drill pipe. These components are fabricated separately from the pipe body and welded onto the pipe at a manufacturing facility. The tool joints provide high-strength, high-pressure threaded connections that are sufficiently robust to survive the rigors of drilling and numerous cycles of tightening and loosening at threads. Tool joints are usually made of steel that has been heat treated to a higher strength than the steel of the tube body.
API spec 5DP
Connect two drill pipes
Grade ：E75 X95 G105 S135
Range: NC26 NC31 NC38 NC40 NC46 NC50 SLH90 PAC