My optometrist could not get my glasses to fit properly, huge frames. I ordered these bands as a last resort to fix my $600 prescription sunglasses. Omg it worked I love my glasses now.

The rings are small, but letting them sit in hot water and then installing them by holding the stem with the earpiece end extended away from you and coaxing the ring towards you by using your two index fingers (fingernails), saw these rings slide over my thicker stems. An alternative to hot water is to use talcum powder which would assist in the sliding of the rings. For the largest stems, I verified that the glasses in question did not have spring-loaded hinges, and installed the ring from the hinge end by simply removing the stem with a jeweler's screw driver and placing the ring on the hinge. (If you have spring loaded hinges, do not attempt to do this unless you have the know-how, or have viewed the YouTube clips on how to re-attach a spring-loaded stem to the frame.)
Because of the one size fits all, you might find that besides the difficulty in sliding the rings over the stem, there might be a situation where the ring when positioned, is not being "pinched" by the stem, when the stem if fully open. You can fine tune these however, by cutting a small, round, eraser tip-size washer out of an old bicycle tube, with a small puncture in the middle. Slide this over the stem to help work with the ring to give you adequate tightening.
Because of the many variables from glasses to glasses, one might not need this amount of stem tightening from the O ring. If the rings fit, but they force the stems inward too much, it might make the glasses too tight on your head, or it might put too much stress on the nose bridge. You might try just the bicycle inner tube; again cutting a patch that is appropriate for your stem size, puncture a hole in the middle, and then slide that onto the stem. I used this technique for one pair of sunglasses that had adequate grip (but wanted a little more so as it slips during physical activity). This technique gives just the right amount of grip, while the inner tube is surprisingly inconspicuous. If you need to keep glasses from slipping, try the rings or inner tube, but also do a search under "no slip silicone nose pads." I'm waiting on a ten pack pair of those from Amazon, which hopefully when combined with the inner tube, will prevent slippage when mountain biking.

I replaced the hanging strap for my drug store reading glasses with these rubber hinge rings. One ring on each hinge tightened up the hold on my (narrow) face. No more slipping, no more catching the glasses as they fall, and no more wrestling matches with the strap. After reading the reviews, I was anxious that the rings would be difficult to put on. I live in the NE and received the package on a cold day. Right out of the cold package, these rings simply rolled up to the hinge. I tried two rings on one hinge and changed my mind- the ring rolled off despite its tight fit. The best part is being able to put the glasses open around my neck and the hinges keep the arms tight enough to hold the glasses securely under my chin when I don't need to use the glasses. BTW, a pair of these rings come with most of the small eyeglass kits sold at the grocery or drug store check out. I used to toss them!

I like the effect as they tighten up the glasses well but they are very hard to slip over the bows as they are too tight to stretch easily. I had to insert some small pliers tips into the ring and stretch it out a bit to get it over the end of the bow.

Use on my glasses at the gym. Tired of losing glasses down my nose when exercising. Hard to find anywhere.