From DT Online
Dowel Centres (aka Dowel Markers) are used accurately to mark the holes to be drilled for a Dowel Joint. They comprise a shank turned to suit the Dowel diameter and a point to mark the centre. When drilling for a Dowel Joint, holes are drilled on one half of the joint into which the Dowel Centres are inserted. The two parts of the joint are then brought together and the points mark the centres of where to drill on the second half.
Features and Applications
Dowel Centres are available commercially (usually in packs of 4 per dowel size) but they are readily machined by anyone with access to a Lathe. Turn the body from Brass for example, then drill to press-fit a pointed length of Hardened and Tempered Silver Steel ideally - although any suitably small diameter steel if only for occasional use.