I'm not certain we answered this very good question, so I'll have a crack at it. The ATN140LC, by the way, is an excellent stylus which does happen to fit and work in the AT120E body.
abhiv0508 said:
So the stylus and the cartridge are two different things?
Yes, in this case and a majority of other fixed-coil/moving-magnet cases. For exceptions, see below..
abhiv0508 said:
If so then why does what cartridge you have matter so much?
For fixed-coil (aka moving-magnet) cartridges like your 120E, the user-replaceable stylus assembly has been the norm for many decades. Once upon a time, though, stylus assemblies were not separate, and once the diamond wore out, the cartridge had either to be tossed out, or else removed from the turntable and sent to the manufacturer to be re-diamonded. This is still the case with most moving-coil cartridges.
Once this "stylus" became a vitally important yet separate assembly that slid or snapped into place, manufacturers often produced one very good quality body which then became many different models depending on which stylus was sold with it.
Your 120E body can accept many different Audio-Technica styli because the same body was sold stamped with the names of all those different styli, and sold at every price point imaginable. Why? The maker then appears to have a cartridge for every need and wallet. What he really has is a
stylus for every need.
"One body, many styli". This makes it simple for the enthusiast who wants the future opportunity of a simple upgrade but doesn't want to have a lot of cartridges mounted in a lot of headshells. Merely swap in a better stylus.
We don't always get this nice treatment from manufacturers. But even when we don't, the strategy is usually "few bodies, many styli". ADC, Pickering/Stanton and Empire are good examples of this. Shure, on the other hand, is an example of the "several bodies, several styli".
This is a simplified picture. As the decades passed and records got better and louder and more dynamic, the engineers would get a good idea for coping with these software improvements and want to make a big hardware improvement, but the old design wasn't flexible enough to accommodate the changes, so they'd start with a clean sheet of paper, change the body's internals and create a new cartridge incompatible with anything before it. So, you often need to know what era a given body comes from so you can match it up with its companion styli.
That's the case with your AT120E, which is a much-improved version of the AT12E, which dates back to around 1972. They look almost the same at first glance. But the 120E body is so different that you can't mount a 12E stylus on it. The new styli are also improved, though, so you're not missing much by having to leave the 12E stylus behind.
abhiv0508 said:
So if I was to search for a styli for an AT-120E, all the ones it comes up with are all options for me?
Yes...
If the sites offering up these options know their stuff. That's the tough part, knowing which sites are knowledgeable enough not to lead you astray, and the tougher part is to find the sites that will correct their mistakes without insulting you and/or making you wait months for a refund/replacement.