Frence cleats inside a toolcabinet for basic handtools

Hi,

I am making a tool cabinet for my hand tools (chisels, saws, measuring/marking tools). Since I am still a beginner woodworker hobbyist and collecting tools I’d like it to be flexible to rearrange to accommodate new tools. I thought I’d used french cleats to hang tools in there. They of course take some depth away from the cabinet compared to juts screwing the tool racks directly to the cabinet, but the flexibility in rearranging the cabinet would probably be more important. However, I don’t want to waste any more depth than necessary so I’m thinking what would be minimum thickness for those french cleats? I know 12 mm (1/2”) would definitely enough for just hanging hand tools (like 10 chisels), but would 9 mm (~3/16”) or even 6.5mm (~1/4”) be enough.