I think your handyman is thinking of something else. You need both length and thread to define a screw.
The diameter of the axle on a regular bike is 10 mm. Most ebike axles are usually 12mm. but what they do is square off two sides so it's 10mm and slides into the slot. The thread on the axle is 12mm x1.25, so if you ever lose the nuts that come with the motor, you're going to have an awful time finding them in the USA. Not carried at Ace or Sears Hardware stores, Lowes, or Home Depot. I haven't lost any, but I ordered some extras off amazon.
If the nuts get loose, all that keeps the axle from spinning is the square edges of the slot. So we put torque arms that fit over the axles and clamp to some convenient point on the frame. Sometimes they use hose clamps. This guy on
amazon has a good price. Here's the torque arms on both sides of my front drive 20" motor. One is home made. The other is store bought. I have never seen a torque arm on a commercial ebike as they will design the forks specifically for holding a motor. You can also see from these pictures that I got so much hardware on the axle, I almost ran out of threads to hold the nuts.
Back to your issue. is it possible they sent you a rear motor wheel instead of a front motor wheel? That would have been an inch too wide. They do claim the front is a 100mm axle width so there should be no problem fitting a standard drop out.
If they included a cluster of gears that would have been been the clincher.
For fun, here's pictures where people used wrenches for a torque arms.
