I saw that episode. They are cup magnets, a magnet in a steel cup that makes the magnet stronger than the bare magnet alone. They have a hole through them for mounting and somebody had just added a nut and bolt to make a handle. The ones on the show looked like 25 lb size. I have a couple. It is a common hardware store item. Just google cup magnet.
I do not recall what they were rebuilding. It might have been the AMX. More to the point, this is what they were using. They had the nut and bolt reversed from mine. These are 25lb magnets, they come in different sizes. They are not neodimium but are quite strong. The cup increases the strength, protects the magnet and gives you something to bolt to, without having to worry about cracking the magnet. Neodimium magnets are very brittle.
