Fountain Pen Revolution Feeds

[Symphing12]

Hi I didn't know where to put this so please delete if this is the wrong place, but...

 

I wanted to know how to pick the right feed for my pen when buying from Fountain Pen Revolution.

 

Here's the link in case anyone wants to see: https://fprevolutionusa.com/collections/5-5-nibs

 

My pen has a feed that is 39mm long but I'm not sure that's what they're measuring here. Any and all help appreciated!

[BaronWulfraed]

Based upon the images at https://fprevolutionusa.com/collections/feeds the measurement is the /diameter/ of the feed.

[Zookie]

Ask Kevin at FPR. I'm sure he can tell you.

[Arkanabar]

Kevin's customer service is stellar. If you email him, you are very likely to get a reply quickly.