Tub Filler Threads: NPT or NPSM for Code? A freestanding tub filler can look simple at first. Yet the thread type can cause real questions. This is especially true in Massachusetts. The common issue is NPT versus NPSM. NPT means National Pipe Taper. NPSM means National Pipe Straight Mechanical. These threads may screw together. That… Continue reading Tub Filler Threads: NPT or NPSM for Code?