I'm measuring the tuning pins in my piano to determine what size tuning hammer is required. I notice the pins taper off with the smallest end on the top and the largest end at the bottom. I'm getting these measurments when using a micrometer.
top (narrow) = 6.22mm (.244")
bottom (before the coil) = 7.25mm (.285")
length (between coil and end) = 1.5mm
I'm thinking a 2/0 hammer would work?
This is a common mistake that people make about tuning pin size and tuning tip size. There is no connection whatsoever.
Tuning pin size (2/0, 3/0, etc.) has to do with the diameter of the threaded portion of the tuning pin.
Given that the head of the tuning tuning pin is tapered -- as is the interior of the tuning hammer (or lever, take your pick) tip is also conical, any tuning tip should fit any tuning pin.
So what is the reason for the tip size of #1, #2, #3? It is to provide a varying "sweet spot" of two opposing parameters to meet the personal preference of the individual technician. Ideally, the fit would be tight on the pin and low on the pin. However the reality is that the choice is 'high and tight' (#1) or 'low and loose' (#3). I can use any tip, but happen to prefer the #3 tip simply because I am most comfortable with "low and loose". This means nothing at all for anyone else. I have other colleagues who use all sizes, heights, and shaft angles of tuning hammer tips. They all work -- and work well. It's just a matter of personal preference.
Where someone has no basis for their own opinion, I suggest starting with a #2 and figure it out from there. Whatever you do, don't stress out over the choice. Most of the theories, philosophies and opinions favoring one height, angle or size over another are inconsequential at best and invalid at worst.