righty, they finally turned up, around a month from ordering, but that is china post for you!
first, this is what they are, keyring openers, cost around $14 for 6 including postage so worked out to i think £1.66 each or around £10.
now the screw to hold them is TINY, even the smallest woodscrew i could find was far too large so dont know if you can even get a woodscrew to fit, but thats something to look at later.
the opener when removed is 31mm and the gap in the middle is 21mm at the widest hole point (for the cap to fit into), so a 33mm forstner and a 22mm forstner fits nicely.
the screw head is 3mm and the countersunk seems to be around 1/2mm, so A REALLY SMALL screw would be needed to make a nice fit.
the metal for the opener isnt the best, it is 1mm metal so adequate but without knowing tolerances i doubt it is suitable for long term use (it is only from a keyring anyway so expectations are that it wont be used that much and if it did break it wouldnt be something to cry over!)
so yes, it works, but you would need to find a more suitable screw for it (probably cost more than the keyring to find), and if you were going to sell it i would suspect this may not be that suitable unless it is for low cost items or novelties.
ignore the dire screw size, but you get the idea!
and a link to where i got them from
http://www.dx.com/p/creative-portable-z ... ver-388878