15MM OD X 4MM ID X 3MM NEODYMIUM MAGNET

These are strong! Bought 10, all are great!

Still, probably for smaller projects but strong enough up to ~120-140mm distance max. I like the through holes, figured it may take a fraction of strength away but gives you cool ideas! Careful, they will chip each other's very outside diameter if you let them clang hard enough. Well worth it. I wonder if those same size discs without the hole is barely stronger? :)