Size 8, 18.54 mm inner diameter. Innovative five-band ring design by Bram Cohen.
Interlocking metal version
(Note that this stainless steel version is not for sale. Shapeways used to print this model successfully in the past, but after swapping suppliers they are able no more. Instead please refer to the interlocking metal or nylon versions.)
Watch the YouTube video
of the nylon version.
Other puzzle rings designed by Bram: