Not sure what t-maxx you have, but traxxas does list out the appropriate bells for their rigs in the manual.
Most of the bells that come to the top on that link are 1M 1/8 scale bells. The maxx/jato run 32P/.8M pitch teeth on their spurs/bells.
You need one of 4118, 4120, 4122, 4124 (18T/20T/22T/24T respectively)