These bearings are a perfect fit in the Tamiya FF02, M03, and M04 chassis's. Just be aware that Yeah racing has said its for the M03, M02, and FF02 chassis's. The M02 should actually be M04 as the M02 is completely different. Still, great product that gets my recommendation.
If you're thinking about racing your M03 mini, you should know that all your competition will have one of these set of bearings installed in their car. This is an instant cheap way for some performance boost to your chassis. A more freely rolling car, means it has less friction, this translate to more speed.