These are increadible caps. They work well with Krylon and Montana, as far as I know. Works on Belton. Gives a fat soft line, it can give a clean medium like if you hold it closer to the "canvas". These caps are very good for fills and outlines.
These caps are very nice for fills. I've used them on Krylon and Rusto paint. It works well with both, but it works much better on the Rusto, hence the name Rusto Fatcap. Very quality caps.
This cap isn't as thin as people make it out to be. I used it on a molotow can, I found that the stock molotow cap was much thinner than this one. It does a really nice medium line though.