Frost plugs

Royal pain in the *** to do this with the engine in the car. Get a kit that uses marine grade brass plugs and you will never do them again.

BTW those are called "core plugs" not frost plugs or freeze plugs. They have nothing to do with an engine block freezing and then popping out to save it. Oh they will pop out when water left in the block freezes, and the block will still be cracked.

They are called core plugs because these holes are where the casting sand was held in place for the water jackets when the engine block was cast. The rough sand cast openings are then machined for a finish plug for the water jacket.