Tool joint:A heavy coupling element for drill pipe.
It is made of special ahoy steel and has 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 leakproof 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 box, is attached to the other end.
The tool joint may be welded to the end of the pipe, screwed on, or both.
A hard-metal facing is often applied in a band around the outside of the tool joint to enable it to resist abrasion from the walls of the borehole.