When seting up my Z axis, I came to a point I wanted to replace the motor/gearbox to increase speed. I needed to measure how much torque the gearbox has to overcome. That is because these things are sold from catalogs listing speed and torque.
I later considered it was a bad idea to increase motor size with higher electrical current load on the shield. That is because there is only so much power the genuine shield can handle. At the risk of overheating.
Coming back to torque: I wanted to measure the needed motor torque. So I disconnected the motor/gearboxx from the shaft coupler. I wrapped a wire around the shaft coupler and attached a bottle filled up of water to try to figure out how heavy the bottle needed to be to start turning the router screw.
There is some initial torque (static friction to overcome), then it can move with less torque. In my case it was in the order of 2.7 kg.cm. Barely turning.
That is why I carefully waxed and adjusted the router clamp latch to not hold the router body and yet not let the router body move sideways (affecting the bit position).
Now that screw thing above is definitely something I want to try tuning.