It is always difficult to fit plugs perfectly; any slight runout in your drill-press quill can make the holes oversize. Unfortunately, this runout will also make plugs undersize. The combination leads to ill-fitting plugs that are very noticeable in your finished work.
Snug-Plug cutters are designed to cut slightly tapered plugs; the first 1/8" of the plug is the stated size (6mm, etc.) and then flares out at a 3° included angle.
Unlike regular plug cutters, they also shave the plug sides as they cut, producing very smooth plugs. You just tap a plug into a hole until you meet resistance, then cut off the excess. You will then have a plug that fits perfectly, with a nearly invisible line between the plug and the workpiece.
These plug cutters are carefully reamed after hardening to ensure perfect concentricity. It is difficult to believe how nice a plugging job you can do until you actually use one.
First 1/8" of plug is stated size (1/4", 5/16", etc.), then flares out at 3° included angle
Cutters carefully reamed after hardening to ensure perfect concentricity