I have used wire mesh wheels with my chinchillas with no trouble as long as the openings are no larger than 1/2 inch x 1/2 inch and the chinchillas are adults. However, some chinchillas have developed spine problems from the arch they have to do to fit in the 12 inch wheel. 15 inch is much safer. Also, there should be no plastic in the chinchilla cage. If the chinchillas chew the plastic and swallow it that can get a fatal blockage.