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The ones I was getting has a small countersunk hole in the middle. I use them for security alarm recessed window contacts. 3/8 diameter.

I think I've got some laying around, let me look.

They're about the size of a smartee (the little candy). And super strong! I had to screw a golf ball to one just so I had something to grab onto...

That brush is amazing! I like a brush with some heft.

Any chance you could hide/recess a neonidium earth magnet in the base? That way you could hang it upside down say from the bottom of a vanity?