National Pipe Straight Mechanical (NPSM) has a straight thread, unlike NPT, which is tapered. NPSM is sometimes used for fluid power systems and male NPTF pipes will seal with an NPSM female pipe. However, a male NPT pipe will not fit in a female NPSM pipe. Being straight, NPSM pipes do not seal as effectively as tapered NPT pipes do. Because of this, they will require sealants to make the connection leak proof. NPSM can be sealed with tape, Pipe Dope, or an O-ring. Frequently NPSM pipes are used as structural pipes instead of transporting liquids or gases, but a sealant is required if those will be transported. Because an NPSM female can accept an NPTF male NPSM pipes are great for piping when versatility is needed.