Understood, but still, was the 36mm reference a guess on your part, or did you see that info somewhere?????
Clearly, the heatsink was designed for use with the Xcelorin motors from Losi and they're actually 39mm as MetalMan stated earlier versus the 36mm I suspected. I would be concerned that there isn't enough room within the heatsink for something like a Castle/Neu at 42mm.