Originally 45s were mono, cut with a one mil groove. All vertical signal
At some point (no pun intended- well, maybe) it matched that of the stereo
LP, even when the signal was mono, i.e., .5 mils.
When did this happen?
I'm not discussing EPs, stereo 45s, etc., just your nommal, get the biuck
out of the teenager's pocket 45.