Industry standards.

Someone in a nearby apartment moved out and divested a lot of their stuff, among which was a jarred candle missing its lid. When I got back to my place, I remembered I had a spare jar lid stashed in my silverware drawer. I don't remember where it came from, and I don't know why I thought it was a good idea to hang onto it, and when I tried it on the jar, it fit. It screws on easily, nicely, and smoothly.

This is doing absolutely nothing to curb my packrat tendencies.