[bonzo]

M3 is the smallest you will find commercially and I'm in a metric country (that's why you only get 1.5 allen keys and not 1). I have seen smaller on McMaster Carr I think though. I retapped my PDI hop for a single M3 grub screw and filled in the two little ones - it's much better now.

 

[bonzo]

I'll measure my one tomorrow morning (in 12hours). Probably the longest one though (5mm).

Should be easy to tap because the hop unit is soft metal like aluminium (= duralim) or maybe brass. Drill a 2.5mm hole and get an intermediate M3 tap. Just use a small adjustable spanner rather than a tap handle (cheap). A cheap/free source of taps is machine shops where their machine taps (also a plus if you can get them because they have flutes like a drill bit so you can tap the hole is a second using a cordless drill) aren't sharp enough for steel but will still chew through soft metals - or get them to do it for you. You can also do an equivelant small size in imperial if that's easier where you are.

I prefer spending a few days fine tuning my hop by adding epoxy and filing it back and then having the simply up/down adjustment forever after. Nearly there with my Firefly bucking.. will post up what I did when it's done.