Threadmilling

[cooliced]

Im wanting to replace the brass valve for a alli manifold.

What would you suggest is the best way of doing this.

the steel but you see i will be keeping.

[Jay]

To cut an NPT thread using a thread mill you need a proper tapered thread mill or you wont be able to form the taper.
What your proposing is a BSP thread so are you sure its NPT?
Because your only wanting to cut 7mm deep you may end up chopping your tap down to get the right form so other than that the thread mill is your only option at the depth your working to bud.