Description of the stainless steel threaded boat deck insert M8 – 316L – CM3368
The CM3368 stainless steel threaded boat deck insert M8 is a sealed fixing solution engineered for decks and cockpit soles. Machined from 316L marine-grade stainless steel, it creates a durable M8 female thread in sandwich or solid deck structures, where a standard screw would gradually loosen or allow water to seep into the core.
Its external self-tapping profile cuts its own thread as it is driven 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 7 mm Allen key through its internal hex socket, and offers an 18 mm usable thread depth for the M8 fixing screw.
At Nauticspares, we primarily supply these inserts for anchoring our 4S seats to the deck. With its larger M8 thread, the CM3368 is the natural choice for more heavily loaded fittings: deck hardware, mooring cleats, padeyes, ski towers, rollbars, biminis, suspended seats or swim ladders. It is a dependable solution for yacht builders, refit yards and owners looking for clean, long-lasting fixing points on board.
Specifications
- Type: Sealed self-tapping threaded insert
- Material: 316L stainless steel
- Internal thread: M8
- Usable thread depth: 18 mm
- Overall length (L): 25 mm
- Head diameter (ØA): 20 mm – countersunk, flush finish
- Spigot diameter (ØB): 14 mm
- Drive: Internal hex socket – 7 mm Allen key
- 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 diameter.
- Coat both the insert and the hole with adhesive or marine sealant, then screw the insert in with a 7 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.
- M8 thread suited to heavier deck fittings.
- 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 CM3368 is the right choice if your fittings call for M8 screws and you need robust, watertight anchoring points on a deck at least 20 mm thick – for seats, cleats, rollbars or bimini frames. Its 316L construction ensures long-term reliability in a marine environment. For lighter hardware using M6 screws, the CM3367 version offers a more compact head; for thinner panels, a through-bolted fixing with a backing plate will be more appropriate.
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 M6 under reference CM3367.
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