I'm sure we looked at the drill out and tap with 5mm and then make grubs up with various holes in them before.

Did we have some concern that when a 5mm grub is drilled out to say 3.5mm ish then the Allen key fitting on the end of the grub would be taken out?

So I can't remember if we said to use grubs with flat driver heads and not Allen key.

I looked at doing that as I was concerned my 3.8TP was too large. I spent some time looking up about aerodynamics and air flow through a port. I was a little concerned about getting a smooth air flow entry on the inside of the piston.

I think I asked if anyone had actually done this or whether it was just theory.

Has anyone actually done this and it's been a success?