HI,
I have 2 907 canisters that we use when camping, the regulator as Antares said just screws on, I usually take the pipe off of the rugulator and screw it on, not having to spin the canister itself. The best way to purchase them, is to buy an empty canister, I got one from ebay, about a £5, then exchanged it for a full one for about £14.00 total less than £20 for a full canister, normal cost when buying from camping shop £55 or so. If you do get one, make sure it has the carry handle that screws where the regulator goes or you could have a problem changing it for a full one.