Galvanized nuts are dipped as blanks and then tapped with an oversize tap, leaving bare internal threads that rely on the zinc on the bolt for protection. The extra clearance cuts thread stripping strength, which is why galvanized structural assemblies use stronger nuts such as A563 DH or A194 2H. Overtapped nuts belong only on galvanized bolts; on a plain bolt they are loose and weak.
Those nuts are overtapped for galv, keep them off the black bolts, they'll strip at half the torque.
Also heard as
- overtapped nut
- oversize tapped
Related terms
HDG
Hot-dip galvanized: coated by dipping in molten zinc, leaving a thick, rugged layer for outdoor steel.
Thread stripping
Failure where the threads of a nut, tapped hole or bolt shear off instead of the bolt breaking.
Nut
An internally threaded part that mates with a bolt or stud, graded so the bolt breaks before the nut strips.