FW Engine Mount Rivet question

Plans for firewall call for 2 different rivet sizes on the engine mount 426 4-6 and 4-7, yet it's the same thickness throughout.

What have others done? Anyone know why if this is correct?

Update: Heard back from Vans, " Looks like a Typo" so I went with the 6, 7 were quite long and proud.

You can't use rivet length callouts as fact, sometimes you need a longer one, sometimes shorter. When I've worked major mods on transport category planes, engineering usually didn't even call out a length, it was as needed. Stick one in there and see if it's the correct length. After doing a few thousand you'll be able to eyeball it.
Anyway all the info is in 43.13