A pipe nipple is a short length of pipe, threaded on one or both ends, used to join two fittings — couplings, valves, tees — into a threaded piping system. It looks simple, and it is, which is exactly why the details matter: the wrong thread standard, the wrong length, or the wrong schedule is one of the most common reasons a shipment gets rejected at receiving.
We cut to Schedule 40, 80, XH and XXH — schedule refers to wall thickness, not length. A higher schedule means thicker pipe wall and a higher pressure rating, not a longer nipple.