Threaded couplings look like simple parts, but a small mistake in size or thread form can slow down a whole pipe job. Before a coupling is used, the first check should be the nominal size. A 1/2 inch coupling and a 3/4 inch coupling may look close when they are mixed in one carton, so clear labels and separate bags are helpful. The second check is the thread type. NPT, BSP, and BSPT are not the same, and forcing the wrong pipe into the coupling can damage both parts.
The surface should also be checked by hand and by sight. A galvanized part should not have heavy lumps inside the thread, because the pipe may not screw in smoothly. A black steel part should be dry and packed in a way that avoids deep scratches during transport. For repair work, buyers often keep several common sizes in stock, so carton marks, size lists, and simple packing photos can save time when the goods arrive at the warehouse.
