I designed this bottle opener to use a 5p coin as it is the smallest British coin (1.8 mm thick with an 18mm diameter) although I am sure that other currency would work if you are not from the UK. the opener would fold into the handle with just enough friction to hold it securely.
I used is a bolt and nut I had lying around with the bolt baing 24.5 mm long and 3 cm diameter. I used an accompanying hex nut that was 5.5 across. but I am sure another bolt could be cut down or the hole drilled out a little larger.
I hope you enjoy and any feedback would be appreciated. (especially this time as development cost me 15p in 5p coins that can not be removed)