Can I use the 3mm adapter on the 100mm Mecanum Wheels RB-Nex-13 ? We would like to use these wheels with Tetrix FTC robot with 4.7mm axle
If you can find a 3mm hub which is compatible, certainly. Unfortunately the manufacturer Nexus only offers hubs which start at 4mm.
Note that the wheel size is quite large to be rotated by a 3mm shaft, and you might want to consider something smaller:
robotshop.com/en/mecanum-whe … -hubs.html
These are directly compatible with 3mm shafts.