These caps are not the same as shown in the photo on the MoreBeer website. The ones they sent me are not finished on the inside of the cap. They are made of .8g less metal and twist on 1/2 turn less. They do not hold carbonation very well. They are worthless for storing beer more than a day. Not the quality I expect fro MoreBeer. In the attached photo, the caps on the right are what I expected, but I got the caps on the left.
As far as I know, these are the caps that do seal. I bought the plastic caps that just seem to have a thin seal of soft paper and every one of them failed. I lost a gallon and a half of good beer. The one growler I sealed with my last metal lid was perfect. Buy these and replace when they rust, saving money on the plastic caps will cost you good beer.
Got these for my 1 Gallon Glass Carboys and they fit perfect, and airtight. Accidentally capped a gallon of mead before it finished fermenting, and both the carboy and the cap held more pressure than they should have, and doing so did not damage either of them.