Clear for the wrench? (Ability to turn the nut by hand or by torque wrench or by hydraulic jack) or clearance between the theoretical wrench and the theoretical nut for machining ?
ittuser - need more info. Is the nut M42 thread? Or - is the nut 42mm across flats?
The standard wrench size for a M42 nut is 65mm, min 65.12, max 1st choice = 65.72, max 2nd choice = 65.92
There is no 42mm wide nut. As per ISO/DIN 272