20mm Flip Off Caps Burr-Free Flip Top Caps Aluminum-Plastic Caps Single Tone Flip Top Seals for Glass Vial 100 Pcs by ZHANXUBIO (20mm, White)

These are perfect, but I wish they weren't necessary. If you have vials to seal, these are better than the ones that rip on their own. As the picture shows, the aluminum does not rip at all, leading to no sharp edges. If you are preparing sterile solutions, these are a must-have over the ones that rip themselves off. Note, however, that they are only the caps. No butyl stopper nor vial. You must get those separately.

These sort of items are notorious for not begin precise to either photos or per any sort of specification. 1) the photo shows a 4-tab 'melted plastic fit top' for lack of a better way to describe. They have a 6 tab top which, if they were 'easy' to flip like commercial vials, I would not complain but they are *hard* to flip off leading to perhaps accidental removal of the entire lid. 2) The 'skirt' is the metal aluminum ring on the top. And they are short according to specs (and other tops on Amazon) by about 10 mils. Why the fuss? If you don't do a perfect job of stopper compression and crimping this yields a weak seal which will avulse when popping the hard-to-remove-top (see #1) . These items appear overly critical perhaps but what preventable failure rate do you want on your vials. Failure of this sort should be zero. I had one failure of cracked glass because of need for excessive compressive force to make up for the short cap skirt. Caused grief and loss of almost a day's time plus the embarrassment and stress to speedily get a new vial to a client. The red ones seemed to have this short skirt problem but that is just my experience.

these can only barely crimp over the lip of a 10 or 30ml vial, must apply too much force. was snapping tops off vials trying for a good bite. avoid this brand

very nice and clean after removing the cap .. wish they had gray and clear

I had to change my rating from 5 ⭐ to 2 ⭐ on these. After at least 35% of the aluminum seals came off while removing the plastic cap I'm done with these for good. Unfortunately I still have about 500 of them. Have a look at the picture. Look how much deeper the yellow and black cap (another brand) is than the red one (this kind). And when you crimp it on the vial it's even more apparent. I still gave these a second star because I loved the burr-free idea. Otherwise they'd have to be only 1 star because at the end of the day they just don't work.