This low profile spacer was designed to mount a Hot Bed MOSFET PCB to a flat surface, allowing some clearance for the leads. This suits a MOSFET with 60x50mm PCB and mounting holes on 52x42mm centres. The holes at each corner are 3mm and include a countersink. There are two flat areas allow mounting with either screws or double-sided tape.

My board is this one (https://www.amazon.co.uk/gp/product/B06W5RJ9LY) based on the HA210N06 MOSFET. This board is widely available under lots of different brand names and the same thing ranges in price from about $10 to $40, so be sure to shop around.