What size allen key to adjust spring tension on Grafton Speed Controllers?

[scant]

I know it's a tiny size. Appreciate the info

Thanks

 

[elite504]

Imperial mate, not metric. I can't recall if it's 1/16" of an inch (I think so, which is basically 1.6mm), but it could be sixty-thou, 0.060" (which is a shade under 1.5mm).
Hopefully a previous owner hasn't rounded the socket out with the wrong sized key....