The flats are actually 1/4 wide so you need 1/4 hex rather than 5/16.
Max Merritt has the ready made tools for $20 or if you have something else to buy from McMaster-Carr you can also buy a standoff with 10-32 threads that has 1/4" flats and is 1" long. Also buy a wooden file handle at the same time.
Drill the threads out of the standoff using a 3/16 drill bit and drill the handle as needed so the standoff can fit as well as have space for the switch shaft to bury inside the handle. Glue the standoff in the handle and have a decent tool for a relatively few $$.
Here is one I made from junk parts almost 40 years ago.
Attach file:
IMG_2656.jpeg (66.48 KB) standoff.jpg (98.52 KB)
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