Replace stock bearings by these high quality ABEC-3 bearings with much higher tolerance and smoothness and feel a much difference in response.
Specifications:
Thrust bearing x 2 (6x14x5mm)
Use in T-REX 600.
If it doesn't specify which ABEC rating, it's likely that's it's ABEC-1. ABEC-3 bearings are much tighter in tolerance than ABEC-1 bearings, thus provide much higher accuracy and smoothness.