Metric EPDM Rubber Brass Insert Well Nuts
What are metric EPDM well nuts? These are well nuts with an EPDM rubber body and a moulded brass insert threaded to metric sizes. They install blind into a drilled hole and seal it as the bolt compresses the rubber, giving a watertight, vibration damping fastening point that accepts metric hardware. That matters on motorcycles, imported marine equipment, and European built machinery, where every fastener on the assembly is metric and an inch thread would leave you sourcing hardware that does not belong there. AlbanyCountyFasteners.com stocks M4, M5, and M6.
Internal Thread:
Why metric well nuts turn up on motorcycles
Fairings and windscreens are the classic application, and the reasons stack up neatly. The panels are plastic or fiberglass, which cracks around rigid fasteners. The bike vibrates constantly, which loosens conventional hardware and fatigues panel material around the mounting points. Water needs to stay out of the holes. And every fastener on a modern motorcycle is metric. A metric well nut answers all four at once: the rubber body cushions the panel and absorbs vibration, the compressed barrel seals the hole, and the brass insert takes the M5 or M6 bolt the bike was designed around. It is why replacement fairing kits so often ship with well nuts included.
Why choose metric EPDM well nuts
- Accepts standard metric bolts on imported and European equipment
- EPDM resists UV, ozone, and weathering in outdoor service
- Brass insert will not rust or seize inside the rubber body
- Cushions plastic and fiberglass panels against cracking
- Seals the hole and damps vibration in one fastener
- Installs and removes with just the bolt, no special tooling
Metric sizes stocked
- M4-0.7 in 12.6mm length
- M5-0.8 in 14mm and 14.1mm lengths
- M6-1.0 in 21.1mm length
- Drill the hole to the outside diameter of the rubber barrel, not the bolt size
- Match length to panel thickness so the rubber bulges correctly behind it
Common applications
- Motorcycle fairings, windscreens, and bodywork panels
- Scooter and imported vehicle trim mounting
- Kayaks, canoes, and marine fittings using metric hardware
- European built machinery and equipment panels
- Imported outdoor and camping equipment
- Fiberglass and plastic panels needing a sealed metric thread
For inch threads, see our EPDM rubber well nuts. Where the joint needs more strength than rubber can give, rivet nuts are the metal alternative.
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Metric Well Nut FAQs
Which metric size do I need for a motorcycle fairing?
M5 and M6 cover most fairing and windscreen mounting, with M5 being the most common. Check the bolt that came out, since the well nut must match the fastener rather than the hole size.
What hole size do I drill?
The outside diameter of the rubber barrel, which is considerably larger than the bolt. Each size specifies its hole diameter. Drilling to the bolt size will not let the well nut in at all.
Can I use an inch bolt in a metric well nut?
No. The brass insert is threaded metric and accepts only metric hardware. Order the insert that matches the bolt you intend to use.
How tight should the bolt be?
Snug and no further. You are compressing rubber, so there is no meaningful torque figure. Overtightening tears the body internally and destroys both the seal and the grip. Use threadlocker rather than extra torque to stop it backing off.
Will these survive on a bike that gets ridden hard?
They are designed for it, which is why fairing kits ship with them. EPDM handles the UV and weather, and the rubber body absorbs vibration that would fatigue a rigid mount. Inspect them at service intervals, since rubber does age.
Can I reuse them after removing a panel?
Usually yes, and that is an advantage over rivet nuts. The rubber takes a set with each cycle though, so if a well nut has been compressed several times or looks deformed, replace it to keep the seal reliable.