Description of the stainless steel threaded deck insert M6 – 316L – CM3367
The CM3367 stainless steel threaded insert M6 is a sealed fixing solution engineered for boat decks and cockpit soles. Machined from 316L marine-grade stainless steel, it creates a durable M6 female thread in sandwich or solid deck structures, where a standard screw would quickly loosen or let water seep into the core.
Its external self-tapping profile cuts its own thread as it is screwed in, while the countersunk head finishes flush with the deck surface. The closed design, combined with a bead of adhesive or sealant during fitting, prevents water ingress into the laminate and greatly extends the service life of the installation. The insert is driven with a 5 mm Allen key through its internal hex socket, and offers an 18 mm usable thread depth for the M6 fixing screw.
At Nauticspares, we primarily supply this insert for anchoring our 4S seats to the deck. Its strength is backed by a conclusive pull-out test at 800 daN, making it suitable for highly loaded fittings: deck hardware, mooring cleats, padeyes, ski towers, rollbars, biminis, suspended seats or swim ladders. It is a reliable choice for yacht builders, refit yards and owners who want clean, long-lasting fixing points on board.
Specifications
- Type: Sealed self-tapping threaded insert
- Material: 316L stainless steel
- Internal thread: M6
- Usable thread depth: 18 mm
- Overall length (L): 25 mm
- Head diameter (ØA): 18 mm – countersunk, flush finish
- Spigot diameter (ØB): 12 mm
- Drive: Internal hex socket – 5 mm Allen key
- Pull-out strength: 800 daN (tested)
- Recommended deck thickness: 20 mm minimum
Installation / Maintenance
Installation:
- Mount the inserts on the fitting jig, place them on their future location and lightly mark the surface: the drilling positions are now defined.
- Drill a pilot hole first, then drill to the specified 18 mm diameter.
- Coat both the insert and the hole with adhesive or marine sealant, then screw the insert in with a 5 mm Allen key until it sits flush.
- Allow the adhesive to cure fully before mounting the accessory.
- A deck or panel thickness of at least 20 mm is recommended for optimal hold.
Maintenance:
- No specific maintenance is required: 316L stainless steel withstands salt spray and the marine environment.
- Periodically check the tightness of the fixing screws and the condition of the seal around the fitting.
Our review
✔️ Pros :
- 316L stainless steel, highly resistant to corrosion at sea.
- Tested pull-out strength of 800 daN.
- Sealed fitting that protects the deck core from water ingress.
- Flush finish for a clean, snag-free deck.
❌ Cons :
- Requires a deck thickness of at least 20 mm.
- Permanent installation, bonded in place.
- Curing time needed before the accessory can be fitted.
Conclusion
The CM3367 is the right choice if you need robust, watertight M6 fixing points on a deck at least 20 mm thick – for instance to secure seats, cleats or bimini fittings. Its 316L construction and 800 daN pull-out rating make it suitable for demanding loads in a marine environment. For thinner panels, a through-bolted fixing with a backing plate will be more appropriate; for heavier hardware requiring larger screws, choose the M8 version (CM3368).
Good to Know
- Primarily used to anchor our 4S seats to the deck.
- Use a marine-grade adhesive or sealant to guarantee watertightness.
- Pair with A4 (316) stainless steel screws to avoid galvanic corrosion.
- Also available in M8 under reference CM3368.
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