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Extrema Ratio Ultramarine NEDU diving knife

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£ 468,95
SKU: ER04.1000.0321-BLK

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Full description

The Extrema Ratio Ultra Marine NEDU is a deluxe diving knife, developed in collaboration with military and civil diving teams. This specific model was developed with the people from the Naval Experimental Diving Unit from the United States. They specifically wanted a knife as a tool, not a weapon. That's why this NEDU version doesn't have a sharp tip. It is ideally suited for use underwater and in difficult and challenging conditions.

The main goal of the Ultramarine project was to make several tools obsolete by having one versatile tool. The blade has two cutting edges, one side of which is partially serrated. The mass of the blade is heavy enough to chop effectively. The back can be used as a hammer. This knife has a special line cutter.

There is a recess in the blade that makes it easy to open oxygen bottles and shackles.

The handle offers an enormous amount of grip. It is made of fibre-reinforced nylon (FRN) and offers unprecedented grip, especially when using neoprene gloves. The shape has also been designed so that it's always easy to determine the position of the knife under poor light conditions.

The design of the holster means it stays tight against the body. A special flap prevents damage to equipment while using the Ultramarine. The knife is always ready for use in a flash. A diamond sharpening stone is stored in the holster.

If you prefer, you can remove the Kydex insert from the nylon sheath and hang it on your belt with one or two Tek-Lok-like clips (included). The Ultramarine also feels right at home on land.

Because a diving knife gets exposed to exceptionally corrosive conditions, the danger of rust is always lurking. Extrema Ratio has opted for an extremely corrosion-resistant steel, namely Böhler N690, but (long-term) exposure to saltwater can always cause extra rust. That's why the blade has a premium coating. As a result, only the edge is at risk of corrosion. For this reason, the knife comes with an eraser that can quickly remove most rust spots. You can sharpen the edge with the supplied diamond sharpener. This is another way to remove rust from the edge.

Naturally, a knife of this quality comes in a good case, so you can store the sheath and all the accessories together.


Finish blade Black Oxide MIL-C-13924
Blade shape spear point
Type of edge partially serrated

Extrema Ratio Ultramarine NEDU diving knife


Features & functions

Finish blade Black Oxide MIL-C-13924
Blade shape spear point
Type of edge partially serrated
Way of sharpening Western sharpening angle, flat, double edged
Type of knife diving knife, tactical knife
Best use tactical, diving
MOLLE-compatible yes
Sharpening angle 30º

General information

Brand Extrema Ratio
Colour black
Can be engraved yes
Country of origin Italy
Warranty on materials and manufacturing defects lifetime


Material handle FRN
Type of steel Böhler N690Co
Material sheath / pouch nylon, kydex
Hardness 58 HRC

Scope of delivery

Sheath yes

Dimensions & weight

Weight 365 grams
Blade height 3.7 cm
Blade length 13.8 cm
Length 27.6 cm
Blade thickness 6.3 mm
Handle length 13.7 cm
£ 468,95

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