I need a tiny set screw.

General
1

So for the sumobot we have these wheel hubs that attach via a set screw to the motor shaft. Unfortunately the motor shaft is a good bit smaller than the hole in the wheel hub. The hub has space for 2 set screws on opposite sides, however it only ships with one set screw. With two set screws we can tighten down on the shaft from both sides and keep the hub centered on the motor shaft.

I stopped by Ace Hardware && another local hardware store (McCabes Do It Center), both of which are typically good at having a wide assortment of parts. However neither store had a small enough set screw. Through testing w/ actual screws I have figured out the set screw is a #4 size, and it looks like it might be compatible w/ a 3mm as well, however I did not test that. Does anyone know of a local store that might sell really tiny set screws? The smallest that either of the two stores sold was a #6.

2

Try a really good hobby store that sells RC airplanes kits and piece parts. A #4 screw has 40 threads per inch (written as 4-40). There are similar size metric screws that are easy to confuse and cross-thread if you put the wrong screw into the wrong hole. Alternately, you could perhaps tap drill and rethread the existing threaded holes to a larger size.

Jim

3

Thanks for the suggestion. I might stop by a hobby store still to see
what they have, but in the mean time I have ordered a box of 4-40 set
screws off Amazon ($5 w/ free shipping). Unfortunately (or
fortunately) this means we will have 98 spare 4-40 set screws.