Thumbwheel for jam-nuts (M5)

I have a situation where the countersunk head of a bolt is hidden and I can't use a screwdriver/allen key to adjust it so I needed to "create" another "head" which I can grip to turn the bolt. I have used two nuts jammed against each other to create the fixed part that can be gripped but to adjust with a finer sensibility I needed something better and larger, hence a thumbwheel.

Because the two nuts, when jammed, are not aligning perfectly, I can't use a plastic insert for both nuts so I chos