How to Make a Knife in Blind Descent

The quick answer

Assemble a Mite Claw Knife in Handcrafting with one Crab Leg, one Mite Claw and one Vine.

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Mite Claw Knife recipe

Slot	Material
Handle	1 Crab Leg
Head	1 Mite Claw
Binder	1 Vine

Assemble the knife

Open Handcrafting and go to the tools tab.
Put the Crab Leg in Handle, the Mite Claw in Head and the Vine in Binder. Press F on Next to move between slots.
Hold F on Assemble. You can equip the Mite Claw Knife once it appears in your inventory.