Jep and they are a real saver if you must cut big openings to fragile materials. Few months ago friend lugged a small countertop to my home and wanted me to open huge hole for a sink. Well, the opening was not huge, but the remaing parts were way under 40 mm on the side and far side. I put the counter top over blue foam insulation on trailler and proceed to cut the opening with plunge/rail saw, leaving just few small tabbs on corners. Then I screwed a board on the "waste" i.e. opening. The board was just a little bigger than hole to support the whole works together during assembly and in the end he had to cut the tabs and undo the board.
This would have been ofcourse a lot easier if he had everything ready and then asked me to cut the hole, but apparently it wasn't designed that way?
Pekka