I just replaced my mazzer mini burr with a new one, when I installed the lower burr back to lower carrier, it seems over tightening the bolt. actually I was carefully screwing it down, but finally I used a little bit more torque to finalize it. I checked thread it seems wasn't destroyed and also burr seems didn't distorted. Does anyone know how much torque can destroy the thread of 3 bore at lower burr carrier? or it's strong enough that the burr will distort before thread be destroyed?

It's not likely that you damaged anything. I'd think the weakest link in the screw, thread, burr system is likely the screw head itself and you'd be more likely to damage the Philips head on the screw before damaging the threads or the burr itself. Are you experiencing any symptoms of misalignment? If so, it's most likely some coffee or other foreign substance between the burr and the carrier - so remove and clean would be in order. The burrs don't need to be held down too tightly, but I don't know how many ft-lbs or newton-meters. I just tighten until it feels good and snug.

Thanks Darilon,

yes I knew that Philips head screw is easy to slip, but MINI is using the slotted head screw which is more stable when applying the torque (since it only need slight axial force to stick the driver to screw head), so I wonder if it's easy to over tighten? Do you know the material of lower burr carrier, iron or aluminum alloy? Have you heard any case about damaging the thread of carrier?

Wow, you are driving yourself crazy. the screw head will break off before your could damage the carrier. it is CNC machined solid chunk of aluminum. the burrs are hardened Swedish steel. the screws are simple stainless. it is not easy to over tighten. I have replaced cleaned and refurbed a few SJs and minis and never saw damaged threads unless cross threaded, usually caused by putting one screw on very tight before lightly tightening the other two.

Thanks Bro, but I think cross threaded will only damage the burr, why can damage the thread? do think the burr will get distort before damage the thread if evenly tight down the 3 screw step-by-step?