Which thread type is described as having a larger diameter and steeper taper, giving it greater strength than the iron-pipe thread?

• A. Mueller
• B. National
• C. Whitworth
• D. BSP

Answer: (A)

Threads with a larger outside diameter and a steeper taper engage more metal and bite more firmly into the mating part. That increased engagement and interference make the joint stronger and less prone to leaks under pressure or pulling forces. In water distribution fittings, Mueller threads are designed with this characteristics—a larger diameter than the iron-pipe (NPT) thread and a steeper taper—so they provide greater mechanical strength for service connections and hydrants. The other standards (National, Whitworth, BSP) have different dimensions and tapers, and they don’t combine larger diameter with a steeper taper in the same way Mueller does, which is why Mueller is described as having greater strength than the iron-pipe thread.