Now you can make your fridge magnets match your cupboard knobs. These rare-earth magnetic bases come in three base sizes, 12mm, 16mm, and 20mm in diameter (approximately 1/2", 5/8" and 3/4") to closely match a range of knob bases, and have attraction forces up to 3 lb, 5 lb and 7 lb respectively.
Available in both M4 (European) and 8-32 (North American) thread sizes.
These bases are also useful for fridge magnet tops made from small turnings, carvings, kids' projects, etc. Just drill a hole in the item to be mounted and put a bit of glue in it for mounting.