Hamster toys can get a bit expensive if you're not sure which ones your pet is going to enjoy. Most hamsters like an exercise wheel, but perhaps yours will prefer an exercise ball, for instance. Make an exercise wheel to see how your hamster likes it before investing in a ready-made one. If you make a really good job of it, perhaps you won't need to buy one. Making a hamster wheel doesn't need to be complicated and you can build one out of items you probably already have. Spend an hour or so and a few cents to potentially save you money.
Solder or glue one of the washers onto the inside of your hamster cage. Attach it to two of the vertical bars. If you glue it, use a very strong glue, like a two-part epoxy resin glue designed for metals. Using the ruler, put the washer at a height of more that the radius of the cookie tin. This way the wheel will be free to turn when it is fixed on. Leave just enough clearance from the bottom of the cage so that the hamster will easily be able to climb onto the wheel. Make sure that the washer, when attached to the two bars, is fixed with the hole between the bars so that the hole is completely free for the bolt to go through.
Take the lid off the cookie tin and discard.
Find the middle of the cookie tin using the ruler. Put a dot there with the permanent marker.
Drill a hole through the middle of the cookie tin.
Thread the remaining washer onto the bolt and through the hole in the cookie tin from the inside.
Push the bolt on through to the other fixed washer when the glue, or the soldered metal, is completely hard and set.
Put the remaining washer on the part of the bolt that is now outside of the cage.
Screw the nut onto the bolt. Make it reasonably tight, but not so tight that the wheel will not turn.
Try and build your hamster wheel in a workshop or shed to avoid causing damage or mess indoors.
Wear protective clothing when making your hamster wheel. Goggles to shield your eyes when drilling the tin and appropriate gloves when using the strong glue or soldering iron will be necessary.