This is the kind of job they would be useful for. I keep meaning to make myself some.
You can see the block supported on the right. Luckily my stepped stepped riser blocks (No idea what the correct name is) worked out to be the correct size on this occasion.
They are deffinately on my to do list.
They are not core drills. The diamond tipped ones are much thinner wall. Thy might possibly be old TCT percussion core drills but they are usually gouged to heck by the time they are worn out.