AN315 nut showing washer face
The previous article I discussed the purpose of the washer face on the bolt head. AN nuts may also (optional for most nuts) use a washer face. It seems obvious that the seating face should be flat, smooth, and perpendicular (within 2 degrees) to the bolt axis.
So how is this design feature of importance to the mechanic? A lot rides on the integrety of this surface:
Face surface influences the tightening tension produced by your torque wrench by controlling friction. It’s estimated that 50% of the friction produced during tightening comes from the bolt head and nut surfaces rather than at the threads.(…)
