Allen Head Plugs

Every pump manifold and unloader has ports you are not using, and each one needs a plug that seals flush and stays put at full pressure. Allen head plugs do that job for a dollar or two. Sun Brite Supply carries them in brass, steel, and 316 stainless from 1/8" to 1/2" MPT. Not sure which thread you are looking at? Call 301-519-9274 and describe the port, and we will get you the right plug the first time.

How to Size an Allen Head Plug

Pipe thread sizes confuse everyone once, because the nominal size does not match what you measure. A 1/4" MPT plug actually measures about 0.54" across the threads, a 1/8" measures about 0.41", a 3/8" about 0.68", and a 1/2" about 0.84". So measure the outside of the male threads on a fitting you know, or the inside of the port, and compare against those numbers instead of trusting your eye. Pressure washer pumps, unloaders, and injectors use tapered NPT ports almost everywhere, and the taper is what makes the seal. Thread the plug in, feel it tighten over the last few turns, and it wedges tight. If a plug spins in loose all the way home, it is either the wrong size or the port is straight thread, and no amount of tape fixes a mismatch.

Brass, Steel, or 316 Stainless

Material matters more than most people expect for a part this small. Brass is the default for water plumbing on the low pressure side, like tank fittings, float valve assemblies, and chemical plumbing. It will not rust and it seals easily against other brass. Steel is the pick for high pressure ports on pumps and manifolds, since it takes more torque and holds ratings brass cannot. The 316 stainless plug earns its higher price around chemicals and coastal work, where sodium hypochlorite eats brass and rusts plated steel. Softwash rigs should treat stainless as cheap insurance. One more rule from the counter: never crank a steel plug into a brass fitting with a long wrench, because the steel threads will win and the brass port loses.

Allen Head Plug Lookup

These are cheap enough to keep spares in the truck box. Call ahead and we will confirm current availability on the sizes you need.

From the Field

Buy plugs two at a time. The first one disappears into the gravel the moment you drop it, and the second one finishes the job. Wrap two or three turns of PTFE tape starting one thread back from the end, so tape shreds never reach your nozzle or injector. On ports you open often, like a winterizing port, snug is enough, since the taper does the sealing and the next guy has to get it back out. And if a hex recess is already rounded out from a worn key, replace the plug now. A rounded plug that later seizes turns a one dollar part into an hour with an extractor.

Related Collections

• Brass pipe fittings and stainless steel pipe fittings
• Steel pipe fittings for high pressure plumbing
• Hex bushings and close nipples
• Caps for sealing male threads
• Tees and 90 degree elbows
• Thread sealant and Loxeal thread locker
• All fittings and adapters
• Need it today? Our Gaithersburg counter can match a sample in person

Frequently Asked Questions

How do I figure out what size allen head plug I need?

Measure the outside diameter of the port's mating threads. About 0.41" is 1/8" NPT, 0.54" is 1/4", 0.68" is 3/8", and 0.84" is 1/2". Or bring the part to the counter and we will thread-check it.

Do allen head plugs need thread tape or sealant?

Yes. NPT threads seal on the taper, but PTFE tape or paste sealant fills the spiral leak path and lets the plug come back out later. Start the tape one thread back so shreds stay out of your plumbing.

When should I pay extra for the stainless plug?

Any time bleach or strong chemicals touch the plumbing. Sodium hypochlorite attacks brass and rusts plated steel, while 316 stainless shrugs it off. On a softwash rig the price difference is nothing against a seized fitting.

What is the advantage over a square head or hex head plug?

The drive is recessed, so the installed plug sits nearly flush. Nothing protrudes to snag hoses, knuckles, or the truck bed, which is why allen plugs are the standard on pump heads and tight manifolds.

Can I reuse an allen head plug?

Usually, if the threads and hex recess are clean. Strip the old tape, re-wrap, and reinstall. Replace it if the recess is rounding or the threads show galling, because the next removal is the one that will fight you.