This is my favorite one, I've had many over the years.
It's just a piece of 1/4" plexiglass that I got cheap as a
remnant from a hardware stores glass department.
It's just holes drilled to fit my router bushing, 3/8" I think.
They don't have to be perfect as long as you register the
template the same way on each cabinet side.
I find a router cuts a better chip free hole than a drill
and I don't have to measure anything.
It's nice to temporarily mark on too with a felt tip that just
wipes off.