Which Allen key for Graham Phantom II Supreme?

Take note of the largest metric allen key that will fit inside the bolt, and then look at this chart.

http://www.metric-conversions.org/length/millimeters-to-inches-table.htm

Look at what falls between the allen key from above and the next size up. That will be the SAE size you need. If you have the room to work, you can get a set of allen keys that are set up like a Swiss Army knife for under $10. Its just easier to go that way, if possible. Also, if this is a really small bolt, shine a light on it and make absolutely sure its an allen key, and not something else, like a torx. It's very easy to mistake them when they're small.

Well, you could either contact Graham and ask them, or buy a set of standard allen wrenches and find out for yourself.

5/64" fits the base screws that hold the pillar in place.

Good Listening

Peter

This should be all you need.

http://www.homedepot.com/p/Husky-SAE-Metric-Folding-Hex-Key-Set-17-Piece-HFHKSM17PC/202934904?N=5yc1vZc265

Zd, god recommendation although I find the the folding sets are rather cumbersome to use especially in tight quarters like around a tonearm etc.

For precision tools my recommendation is Wiha Tools which offers amazing quality and relatively good pricing. For an example a single 5/64" Allen head screwdriver is only $4 + shipping etc., a complete set of Allen screwdrivers only $32.80 as with anything you get what you pay for these are high quality professional grade tools.

More information here Wiha Tools

Best of Luck

Peter