Well Nuts

What are well nuts? Well nuts are rubber bodied fasteners with a brass nut moulded into the closed end. You push one into a drilled hole so only the flange shows, then thread a bolt into the brass insert. As the bolt draws the nut upward, the rubber barrel compresses and bulges out behind the workpiece, gripping the hole and sealing it at the same time. That gives you three things at once: a threaded fastening point in thin or blind material, a watertight seal, and rubber isolation against vibration. Also called rubnuts, rawlnuts, or rubber expansion nuts. AlbanyCountyFasteners.com stocks EPDM rubber well nuts with brass inserts in inch and metric.

Well Nuts

Well nut or rivet nut: which do I need?

Both give you a thread in thin material from one side, but they solve different problems. A rivet nut is metal, so it is stronger, permanent once set, and needs a dedicated tool to install. A well nut is rubber around a brass thread, so it is weaker, but it seals the hole, damps vibration, insulates electrically between dissimilar metals, and installs with nothing more than the bolt itself. Choose the rivet nut when load is the priority. Choose the well nut when the hole has to keep water out, when the mounting is going to shake, or when you are fastening into fiberglass or plastic that would crack under a rigid metal insert. On a boat or a kayak, that usually means a well nut.

Why choose well nuts

Watertight and airtight seal formed by the rubber body itself
Absorbs vibration and noise instead of transmitting it through the joint
Installs blind from one side with no special tool, just the bolt
Removable, unlike a set rivet nut, by simply backing the bolt out
Electrically isolates the bolt from the panel, preventing galvanic corrosion
Spreads load in fiberglass and plastic where a rigid insert would crack the material

How to install a well nut

Drill the hole to match the outside diameter of the rubber barrel
Push the well nut in until the flange sits flat on the surface
Pass the bolt through the part you are mounting, with a washer under the head
Thread into the brass insert and tighten until the rubber compresses and grips
Stop when it is snug, since overtightening tears the rubber and destroys the seal
Use threadlocker, because a bolt that backs off lets the rubber relax and breaks the seal

Common applications

Boat hulls, kayaks, and marine fittings where the hole must stay watertight
Motorcycle fairings, windscreens, and bodywork subject to vibration
Fiberglass and plastic panels that would crack under a rigid fastener
Instrument and gauge mounting where vibration isolation matters
Automotive trim, panels, and accessory mounting
Outdoor equipment and camping gear needing sealed blind fastening

Where load matters more than sealing, see our rivet nuts, which are stronger but permanent and unsealed. For threads in solid wood rather than thin panel, look at thread inserts for wood.

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Well Nut FAQs

Are well nuts waterproof?

They seal well when installed correctly, and that is their main purpose. The rubber compresses against the hole wall and behind the panel, closing the gap around the bolt. Two things break that seal: overtightening, which tears the rubber, and the bolt working loose, which lets the rubber relax back toward its original shape. Rubber also degrades over years of UV and weather, so a well nut is water resistant for a long service life rather than permanently waterproof.

What size hole do I drill?

Match the outside diameter of the rubber barrel, not the bolt size. Each well nut specifies its hole diameter. Too large and the rubber cannot grip or seal. Too small and you will not get the barrel in without damaging it.

How strong are well nuts?

Light to medium duty. The grip comes entirely from deformed rubber pressing against the hole, so pull-out strength is far lower than a metal insert. They are the right answer for panels, fairings, and trim, and the wrong answer for structural or load bearing joints.

Can well nuts be removed and reused?

Yes, which is a real advantage over rivet nuts. Back the bolt out, the rubber relaxes, and the nut pulls free. Reuse is possible, though the rubber takes a set with each cycle, so sealing performance degrades over repeated installations.

Why use threadlocker with a well nut?

Because the seal depends on the bolt staying tight. If vibration backs the bolt off even slightly, the rubber begins returning to its original shape and the seal opens. Threadlocker keeps the compression constant.

Do well nuts prevent galvanic corrosion?

They help. The rubber body separates the bolt from the panel, so dissimilar metals never touch directly. That is useful on aluminum boats and where stainless hardware meets an aluminum or steel structure.