On the full crankshaft 160cc engines, as Blue says, that's the thread size. The nut hex size is 1" AF/SAE, on those 160's.
The half-crank Powertorque engine uses ISO Metric threads, and the corresponding nut hex sizes. For that nut, the thread is 14mm, but dunno what pitch or exact hex size - it will be one of the common metric hexes though.
But I haven't worked on a Powertorque, and have no particular desire to do so!
