Ortlieb Quick rack stay diameter

TLDR; What's the diameter of the rod on the Ortlieb Quick lock seat post mount?

https://uk.ortlieb.com/products/seat-post-mount-mounting-brace-300-mm

I have a Tubus Evo for my Salsa Warroad, but no Rack lock collar to attach to the seat post.
The Ortlieb Quick lock seat post mount looks ideal and can be bought as a spare.
Will it fit my evo?
https://www.tubus.com/en/products/rear-carriers/tubus-product/fly-evo

I just need the diameter of the Ortlieb stay.

TIA