ASME B16.14

Covers — ferrous threaded accessories:

• Square head, hex head, and flush (countersunk) pipe plugs.
• Flush and outside-head bushings (used to reduce thread sizes).
• Locknuts for securing threaded connections.
• Thread forms must be NPT per ASME B1.20.1.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Heavy-duty forged plugs designed to meet Class 3000/6000 ratings → ASME B16.11.
• Main pressure boundary fittings (elbows, tees) → ASME B16.3 / B16.4 / B16.11.

B16.14 focuses on ensuring the heads of these minor components will not shear off during installation:

• Head Dimensions — Because these components are often threaded into higher-rated fittings, B16.14 ensures the physical dimensions of the square or hex heads are robust enough to withstand the severe torque required for sealing tapered NPT threads without stripping or shearing off the head.
• Material — Allows for cast iron, malleable iron, or steel depending on the pressure rating required by the designer.

Plugs and bushings are ubiquitous in piping systems for closing off drain/vent valves, instrumentation taps, or adapting pressure gauges to different port sizes. While ASME B16.11 covers heavy-duty forged threaded fittings (like tees, elbows, and couplings), B16.14 is the standard that specifically covers these minor accessory items.

The standard provides dimensional tables that ensure a wrench will perfectly fit the plug head, and that the threaded length is sufficient to engage fully into the mating female component.