21282
I was just given an old South Bend Lathe. It's a 13" by 6', Serial Number 21282.
It has an odd custom overhead drive,
standard change gears,
sold by the "Smith, Booth, Usher Co." out of Los Angeles, CA.
 that is what a brass triangular shaped tag states just below the threading chart,
which goes from 4-40 TPI. 
Just thought I'd send you a little more information than I had when I posted on the Practical Machinist's
website under "Knolltop Farms", which is the name of our family farm
here in the "49er Gold County" of California's Sierra-Nevada Mountains.
Thanks for the work you do...Aloha, Chuck