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API 7-2 Rotary Pin Connection
A tool joint is a heavy coupling element welded to the drill pipe body which is made of special alloy steel. Tool joints have coarse, tapered threads and seating shoulders designed to sustain the weight of the drill stem, withstand the strain of frequent coupling and uncoupling, and provide a leak-proof seal.
The male section of the joint, or the pin, is attached to one end of a length of drill pipe, and the female section, or the box, is attached to the other end.
Drill pipe, and most tubular products, are run into the hole pin, or male end, down so that the box, or female end, is looking up. This convention is primarily to prevent thread damage and aid make-up by providing a better target for stabbing which is the insertion of the pin into the box end.