What fitting is this?

In the pictures you can see one of the fittings that came in a fitting assortment I purchased. Alongside one of the plugs that came with the master cylinder. The plug has a slightly finer thread. 0.54 diamater. I'm trying to work out the thread pitch.

View attachment 1715750900

View attachment 1715750901
The one on the right looks like the one that is used on my master cylinder with 3/16 line. I suspect the one on the left is for larger line?