These are adapters with the center hole vertically offset by 0.25mm and 0.5mm.

The standard QC holder has a 3.45mm inside bore. If used with round graver stock with a 3.0 or 2.45mm diameter, the center of the graver will be 0.225 and 0.5mm too low, and the top and bottom relief tapering won't be symmetrical.

The clearance on these is set to zero, with the expectation that they'll be sanded and filed (inside and out) for a smoother fit.