I've come across Whitfield a number of times on old mowers as well. There are not only different threads but different pitches among the threads. It can get very confusing trying to match up nuts with bolts at times. My father left behind a large bucket of bolts from the olden days that I still haven't properly sorted. There is a mix of just about every thread. I sometimes pick up a bolt or a nut but am unable to find a match for it.
