Centres three holes and guides the drill bit 

with drilling bushes.

Aluminium body with hardened steel guide bushes

30mm maximum thickness, three 10.3mm holes at 35mm centres.

and One 10.3mm  M35 grade Cobalt drill bit 

and Alen key for tightening.

Reducing sleeve

Brass reducing sleeve for drilling steel string tuners

6.7mm hole, 10mm diameter, 14mm long with 12mm flange

sold in packs of three. with 6.7mm M35 cobalt drill bit.

it's reasonably rigid and the screws can be tightened to make the movement firmer.