om54: Careful there - at least in case of line-contact needles you can't directly conclude from major radius to needle width anymore, because in case of these the reference point for the curvature radii isn't the intersection of the two perpendiculars onto the contact points with the groove walls. Instead, the reference points for each side are just somewhere on the corresponding perpendicular, and in case of pretty large major radii these points may actually be outside of the tip. So in that case all one can tell is that the distance between the two contact points will most likely be up to ca. 25 µm (1 mil), because that's what a couple of record standards allow as instantaneous minimum groove width (at the top of the groove) for microgroove stereo LPs.
Even the manufacturers sometimes would appear somewhat dimensionally confused, though. For example, if you check the two sphericals in Namikii's current "contact area" table over on
https://www.ad-na.com/en/product/jewel/product/stylus.html and look at the first row (front view) and then the second row (A - A'), you'll easily notice that, if the front view dimensions actually apply, the A - A' radius dimensions can't apply at the same time, as the radii in the A - A' plane would rather have to be the given radii divided by square root of 2. So that A - A' would merely apply to how the cross-section in that plane would look, while the given radii would be the (minor) radii as seen from the reference points instead.
Well, and if one does math, actual A to A' distance (i.e. distance between the contact points) for an 0.7 mil/18 µm spherical tip would simply be 18 µm times the square root of two, which happens to be not quite 25.5 µm.
Greetings from Munich!
My browser wouldn't let me go to the site you posted but I think I understand what you said. Probably why shure HE stylus were 1.5 mils. I see why some complain of more surface noise if the tip goes to the top of the groove. Does the tip get closer to the bottom as it wears or shave off the top of the groove? Salutations from the Front Range! (Rockies)
Manfred / lini