I found a light alloy tube - originally part of a cigarette lighter that was the size and shape of a cigarette. Made holes in it to take a split ring, then wrapped the duct tape around it.
I am leary of putting stuff in my wallet. I find it quickly gets too thick. For a while I carried a fresnel lens in it, but it was too thick, and duct tape tends to be thicker. A bunch of stuff loose or on a keyring seems to take less room.
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Quality is addictive.