Guys...I don't want to be argumentative, just curious...
How did they (Cox, or anybody else for that matter ) manage to get such close tolerances without such things as CNC machines? Hand fitting?
I worked in a fully equipped machine shop for a few years (until my mom had a stroke, so I'm taking time off to take care of her ) and ran parts on CNC lathes and mills, and the closest we ever bothered with was 5 tenths (half a thou )

Even 25 millionths...just one little spec of dust under the micrometer and that would throw off youir reading...right?!?