EPDM Rubber Brass Insert Well Nuts

Why EPDM and brass rather than cheaper materials?

Because a well nut lives in exactly the conditions that destroy ordinary materials. It is chosen for outdoor and marine work, which means constant UV, salt spray, and temperature cycling, and the seal depends entirely on the rubber staying elastic. Natural rubber and cheaper elastomers harden and crack under sustained sunlight within a few seasons, and once the body goes brittle the seal is gone and the grip follows. EPDM is formulated specifically for that exposure. The brass insert matters for the same reason: a plated steel thread sealed inside a damp rubber body would eventually corrode and seize the bolt, at which point removal means destroying the well nut and possibly the hole.

Why choose EPDM brass insert well nuts

• EPDM resists UV, ozone, and weathering far better than standard rubber
• Brass insert will not rust or seize inside the rubber body
• Watertight seal formed as the rubber compresses in the hole
• Absorbs vibration and shock instead of transmitting it to the panel
• Installs blind with only a bolt, no special tooling
• Removable by backing the bolt out

Inch sizes stocked

• #6-32 in 0.499 and 0.981 inch lengths
• #8-32 in 0.499 inch length
• #10-32 in 0.554, 0.665, and 0.825 inch lengths
• 1/4-20 in 0.831 and 1.051 inch lengths
• 5/16-18 in 0.725 inch and 3/8-16 in 1.062 inch
• Match the length to your panel thickness so the rubber bulges behind it correctly

Common applications

• Boat hulls, kayaks, and deck fittings needing a watertight hole
• Motorcycle fairings, windscreens, and bodywork
• Fiberglass and plastic panels prone to cracking under rigid fasteners
• Marine electronics, gauges, and instrument mounting
• Outdoor equipment, camping gear, and trailer accessories
• Automotive trim and accessory mounting on thin sheet

For metric hardware, see our metric EPDM well nuts. Where load matters more than sealing, rivet nuts carry considerably more.

Related Categories

• Well Nuts
• Metric EPDM Well Nuts
• Rivet Nuts
• Thread Inserts
• Closed End Rivets

EPDM Well Nut FAQs

What is EPDM rubber?

Ethylene propylene diene monomer, a synthetic rubber with excellent resistance to UV, ozone, weathering, and temperature extremes. It is the same material used in roofing membranes and exterior door seals, which is why it suits fasteners that live outdoors.

How do I choose the right length?

Match it to the thickness of the material you are fastening through. The rubber needs enough length behind the panel to bulge and grip. Too long and it may not compress fully, too short and it will not reach past the panel to form the lip.

How tight should I do the bolt up?

Snug, then stop. You are compressing rubber, not clamping metal, so there is no meaningful torque spec. Tighten until the joint feels solid and the flange is seated. Going further tears the rubber internally and ruins the seal without adding grip.

Can I use these in fiberglass?

Yes, and it is one of the best uses for them. Fiberglass cracks around rigid fasteners under load and vibration, while the rubber body spreads pressure and flexes with the panel. This is standard practice for kayak and boat fittings.

Will the brass insert corrode in salt water?

Brass holds up well in marine conditions and is the reason it is used here rather than plated steel. Extended saltwater immersion can cause dezincification over years, but for typical above waterline marine use the insert outlasts the rubber.

Can I paint over a well nut?

The flange can be painted, though paint on rubber tends to crack as the material flexes. If appearance matters, choose a colour matched fastener or cover the flange with the mounted component rather than painting it.