https://www.lowes.com/pd/Amerimax-Al...E&gclsrc=aw.ds
this might work to cut a shim from, and it's aluminum, like the bars and stem. and cheap. if you have a micrometer, are cheap like me, and have the time, take your micrometer to the local hardware/home improvement/local gutter installers and take measurements till you find something that works. (aluminum shim = not having to worry about dissimilar metal corrosion).