Hi.
The valves to be carved as in the third picture are bronze, nickel plated. The stepped shaft will be center-guided contacting only the wall of its 7mm hole, not reaching its bottom where a 3000psi teflon gasket resides. Should work well.

 

The shaft is to keep this saw centered instead/in place of its drill bit
View attachment 128595
while carving a gland like this
View attachment 128596


to add an o-ring in this valve that has a 7mm center hole :
View attachment 128597

Will that annular cutter give a good enough finish for an "o"ring? That looks like a Hougen or Blair "rotobroach". Commonly used in autobody repair as a spotweld cutter. I've also used the bigger ones instead of hole saws in thick materials, and didn't get anywhere near the finish that an O ring requires to seal at that high(3000 psi) pressure. And that was in a milling machine not a hand held drill.

 

The teeth ground to conform