Countersink sleeves are sized to the bit, not sold as a fixed set

A drilled hole in glass has a sharp rim. It chips when the sheet is moved, and it chips again when a fitting is pulled through it. A countersink sleeve run over the hole after drilling removes that edge, so the chamfer takes the load instead of the rim.

Sleeves are matched to the drill bit rather than sold as a fixed set: a 22 mm hole needs the sleeve that fits 22 mm, not whichever one happens to be in the box. The range follows the bits from 3 mm to 150 mm, with other sizes made to drawing.

They fit glass drilling machines and bench drills, and swap with the bit on the same spindle — the drilling and the countersinking happen without re-chucking.