Replacement Allen wrench.
In the drop-down menu, choose the color of the standoffs on your shedding device to get the correct hex key. The standoffs are the pieces that hold the two thin metal bars on the shedding device. Older looms will have copper-colored standoffs. Newer looms will have silver-colored standoffs.
Copper-colored: 7/64ths hex key
Silver-colored: 9/64ths hex key