I redrilled mine and taped to 10/32. Now I use standard cap screws on mine. I can get them in different lengths at the hardware store.

It is the same diameter of a screw as say a 8-32 or 8-36, but the thread is finer. I don't know if that is what you were asking, and if it isn't, feel free to ask more. If you need to know a supplier, let me know.

Thanks for the answer but thats not what I was asking.8x32 is UNC and 8x38 is UNF. SO if I buy a set of UNC & UNF taps & dies I will get those in the set(supposing the range of the set covers them). Both UNF & UNC are standard US thread series. But I cannot find a standard thread series that includes 8x40. so my Q is it part of a standard I cant find or is it a one off (special) adopted by the gun trade in US or something else?

8x40 and 6x48 are common on US firearms especially on scope mounts and such. I've not seen them used outside the gun industry but it's possible. I get mine from Brownells.

Try a Westlake Ace Hardware store.