There are very few that actually fit(assuming you have the RWD Rustler). Many have said the integy single fan heat sink fits. I didn’t use it because I didn’t feel like wiring up another device. I bought these heatsinks and with some patience and a hacksaw, cut to a size that fit juuuuuuuust perfectly even with the wheelie bar mount. Two things I suggest either way are use some thermal grease under the heat sink as that air gap acts an insulator instead of a dissipator, and if you run it off-road, put a zip-tie around the heat sink because that friction mount just doesn’t hold up to any jumps or rolls.

This is a 4 pack I bought since I also put these in my e-maxx, but they also sell singles and 2 packs. https://www.amazon.com/dp/B07FLHT52V/ref=cm_sw_r_cp_api_glc_fabc_gIDaGb2ACWQ3R?_encoding=UTF8&psc=1

Here is my modified one: https://imgur.com/gallery/zuQDbaW