This is my Knex Knife, and in my opinion the strongest knife here. It is based off of the US Army standard issue M9 bayonet/utility knife. And before you ask, yes you can actually use it as a bayonet for knex guns.
Now for the pros and cons
Easily modded to have any length blade you want.
Can also be used as a throwing knife.
Uses a lot of orange connectors
Now onto building.
Step 1: Parts List
To start, you will need all of these pieces:
Bendy grey: 1
Grey (or black if preferred): 2
Light grey: 2
Oranges: 19 (warned you)
Male Ball Joint: 3
Grey Spacer: 1
Blue Spacer: 1
Step 2: Building the Knife
Step 1: Build, one white con with the two yellow rods.
Step 2: Build, one white rod with grey connector on and male ball joint on the end.
Step 3: Combine the two together.
Step 4: Add, must have the blue spacer.
Step 5: Add the two yellow cons and a grey rod.
Step 6: Add two red rods and the last white con to keep things together.
Step 7: Add an orange con and the last grey rod, make sure you have the grey spacer between the yellow and white cons.
Step 8: Add the bendy rod, it and the grey rod will be the "frame" of the blade.
Step 9: Pit on the remaining 17 oranges for the blade, make sure they connect to the outer grey and bendy rods with the center grey going through them.
Step 10: Put the light grey connector and a mall ball joint on, the light grey con keeps the tips of the rods together and gives the blade shape while the male ball joint keeps the center rod from moving around.
Step 11: Add the final male ball joint to the bendy rod and the green rod to the orange con.
Step 12: Put on the rest of the red rods and you are done.
Hurray! Your finished and now have a very nice knex knife.