With or without flange? The flange (or disk) behind the ear helps keep large / heavy earrings upright and flat against the ear, instead of tilting forward with an awkward sag. Thin or aging earlobes may droop even with relatively light earrings, and the flange (disk) behind the ear really helps the earlobe and earring stay straighter. Some people also say the flange makes it easier for them to put on and take off their earrings.
Rubber or mechanical grip?
The rubber grip is less expensive, and may be easier to fit onto a wider variety of post sizes. But eventually (in a few years or maybe a decade, depending on what it is exposed to) it breaks down and doesn't grip as well. For trendy fashions or delicate materials that won't be worn in 10 years, no problem!
The mechanical grip is a bit more expensive, but it fits all the posts we sell, has a nice springy grip that's easy to put on and take off, but holds well -- and it lasts pretty much forever. We have been selling these since the 1980's (do you remember the crazy big earrings we wore in the 80's? ... if you're too young, watch some of the 80's pop music videos for a laugh), and the old earrings in my jewelry box are still holding strong!
If you have it narrowed down to 2 different aluminum earring nuts with mechanical grip and flange, and they seem almost the same ... well, they used to be a bit more different from each other. With slight manufacturing changes over the years, to remove nickel (without adding other allergens, and still keep their durability, and be a good color match for common jewelry finishes), now they're almost the same. You will probably be happy with either option -- They're both good quality! However, the more-expensive one really is our customers' favorite for high-end earring earrings.
To adjust the fit of an earring nut:
All our earring back normally fit all our earring posts. However, if you have purchased thicker posts elsewhere, or if you have a batch that is fitting a bit too tightly, you can use an awl or a push pin to slightly enlarge the hole in butterfly-style earring nuts. This works best with butterfly nuts, but sometimes works with other styles of earring backs, too.
Lightweight sterling silver butterfly nuts may loosen with use, over time. Just squeeze the curls with finger pressure to re-tighten them. This happens with other metals and weights too, but takes more years to occur.