The preset holes in the Oak Park Mitre Gauge are for centering pins on ½” and ¾” thick wood.
You can make dovetail pins on thicker wood (as shown below) but they will not be centered.
Dovetail On Thick Stock
Dovetail On Thick Stock In Slot
You can not use undersized wood to make a dovetail joint because a square shoulder will appear on both points of the dovetail pin (as shown below)and it will not fit in the slot.