I designed these bases with 6mm in mind for Playing "I Ain't Been Shot Mum" by Two Fat Lardies. The Base dials are the to keep track of casualties while the shock dial is to keep track of shock. each base and dial has a spot to include a super magnet to keep the dial and base together but allow for spin. The magnet size is 6mm round and 1.5mm thick or 1/4" round and 1/16" thick. I think this is over kill but I had a lot of that size on hand and it works.