Can u use the 8mm stub axles with the rpm carriers?
If you can match the inner and outer wheel bearing size to accept the 8mm stub, yes.
I don’t use RPM carriers anymore so I haven’t tried them to see but I’m sure it can be made to work.
For you Dub;
New Traxxas 17mm splined hex, you can see the step inside the bore.
With the stock stub axle there is still a little slop even when new and where the threads ride against the stepped down diameter of the hex the threads of the stub axle will wear away the aluminum and the slop gets worse and worse over time.
I prefer to make my own bushings using ¼ in aluminum rod, but you can use a variety of different metals. The brass 5mm inserts like these (
http://www.tonysscrews.com/product.sc?productId=788&categoryId=12) are already threaded and just need to be turned down to fit.
I drill and tap the rod to 5 x .08mm then thread it onto a 3.3 spec stub axle that has been removed from the yoke. I chuck the stub axle in a drill press and turn the diameter of the ¼ inch aluminum down to 6mm smooth with the stub axle.
This one is just an excess piece I cut off while making a batch and is just a little short.
Once you have the bushing fitted to the stub, you would then need to bore the hex through and through to 6mm removing the step down in diameter.
The original 17mm splined hexes did not have a set down and would not need drilled.