I've just been struggling with the same thing, although I settled on purchasing a Wilkos S/Steel biscuit tin for about £3.99. I used the bick of my anvil to depress the lugs, but one of my bretheren took them off totally and used a ring of brake cable to attach another brake cable handle to, so that the whole assembly can be easily removed if neccessary.
Anyway.........I digress
, I believe the ID of the biscuit tin in question is 13.5 cm.
I hope this helps!
EDIT: Just added a photo to give you a rough idea of the size comparison with the 12cm zebra billy. A 10cm billy
may fit comfortably without removing the handle!!