Wellllll......there actually NOT freeze plugs, although they will pop out if the coolant freezes. They're core plugs where the manufacturer dumps out the sand after the casting cools. And if you're depending on them to keep your block from cracking when it freezes, you may be in for a very $$$$$ mistake. I've seen many cracked blocks where the core plugs were pushed out, & a few where they stayed in.
Most core plugs rust from the inside out due to corrosive contaminants in the coolant. They also do tremendous damage to aluminum parts. The additives in anti-freeze help keep that from happening. For best results use only anti-freeze/coolant & distilled water.
One more reason I don't want a water cooled bike.