https://www.amazon.com/d/Home-Storage-Organization/Perfect-Curve-CapRack-System-18-Caps/B001R5TTVI

https://www.amazon.com/CapRack18-Baseball-Cap-Holder-Black/dp/B001DTA6MY

First one has big plastic clips which hold everything securely and let you do 3 per clip, plus it makes them stick out a bit. Second one is a bit more simple and the hats hang down. I've got 3 of that one on my door for my ivy caps.