Here's a simple 3D printed grappling hook. It depends how much you want it thick, and how heavy you are, but the hook probably won't support you when mountain climbing...
You will need:
-Access to a 3D printer
-A little bit of knot-tying skills.
Step 1: Make the Base
Using 123d, make a rectangle 20 by 20 by 70 (you don't have to use 70, you can choose the height.)
Step 2: Use Draw to Draw Squares on the Top Sides of the Rectangle
Using the draw function, draw squares on the top sides of the rectangle. Enough said.
Step 3: Extrude Each Box
Use the extrude function to extrude each square. Extrude it by 40mm.
Step 4: Draw on the Hook Like in the Picture
Draw rectangles on the hooks like in the picture. It's easier that way.
Step 5: Extrude Those Rectangles Backwards
For each rectangle, do extrude -20.
Step 6: Draw a Circle, and Extrude It Backwards.
For the hole for the para cord, draw a circle, and extrude it -20.
Step 7: Merge the Project
Merge all the pieces together.
Step 8: Tie the Para Cord to the Grappling Hook
Tie the para cord to the grappling hook through the hole.