I ended buying at bag of 100 at Amazon. I needed them because I had to add a Reptilia plate. I bought a native cut slide and bought and installed suppressor sights, but I forgot that a native RMR cut puts the sight much lower than a MOS. The iron sights obscured the optic. Rather than getting and installing a new set of sights, I threw a Reptilia plate under that RMR. Leaving my sad life story aside, I now have a little bag with 98 screws. They were made from the best chinesium the money can buy and I had no issues.
Just in case, the size was
#4-40 x 3/8" Flat Head
https://www.amazon.com/gp/product/B01LXDH8ZI/