For M3 stainless steel nut that are 5.5mm wide.
I tried the other thumb wheel on here, but it did not fit the M3 nuts I got from my local Ace Hardware.
I used a black Sharpie marker to give some contrast.
November 2016 UPDATE: I have a new design that is smaller, a bit pointier, and works with more printers. Check it out here: small thumbwheels