[Closed] Switchback riders

I know there are a few out there who have one of these so hopefully someone can help.

Using a shimano e-thru axle on the rear, but the nut that you tighten into is not fixed to the dropout, take the axle out the nut falls out too.

Has anyone just left it like this or have you got a wee grub screw that keeps this nut in place, if so what size grub screw is it?

Cheers