i have seen some on FJ they have the same tubes as the Pro rack
here are two different ways to go
DIY FJ Cruiser Roof Rack Axe, Shovel and Tool Mount | by J&J Kniv Supply Co. | Overland Expeditions and Journal | Medium
4x4 Roof Racks for Sale | Off Road Roof Racks
I built something like this for my Gobi rack. It should work for the Pro rack. I made two of them which you can mount in series depending on the length handles of your axe/shovels.
Here's the write-up DIY Axe Shovel Mount | Toyota FJ Cruiser Forum
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How is the left quick fist mounted to the plate? I see the nut hanging below on the right one. Did you counter sink something?