Lou Judson • Intuitive Audio 415-883-2689
In their original paper on the format, RCA specified "...a 1-mil radius as the minimum for the reproducer stylus and a 90-degree, 0.25-mil bottom radius groove" with a tracking force of not more than 5 grams. A PDF of the paper is here:
http://tildebang.com/jukebox/rec_and_changer_comp_design_45.pdf