awhile ago I posted about my master cylinder screw not able to get out, but now I took it out but I need a replacement and I don’t know where to get one, I am still new to this and a noob , also its a 5mm 
Post a pic of the master cylinder and the kart make/ model.
is this one #27: P/N VLE3400: 0039 Master Cylinder - RLV and I think the kart should be vlr
It is likely this one. Measure the thread size with verniers and if it’s 10mm it should be right.
You gotta love Monda. When I need something like that from then I order 3. 1 to keep as a spare and 1 to give someone at the track that is a jam.