The thread size is M5. The schrader valve is a custom made part for VEX. We do intend to sell the various “jewel cases” in the pneumatics kit, so it’s coming. I don’t have an exact timeline, but I’m hoping we’ll have some in stock by end of the year.
And yes, M5 thread fittings can break if they are torqued too much. Be careful, the fittings will seal well below the breaking point. Snug is good enough.