shim material for shock arms

[1930artdeco]

Quick question, When I pulled the dif I noticed that both rear shock arms were extremely loose on the shock stud. What can I use to shim up the arms to tighten them up/ideas? I noticed that both arms were clamped down so there is no gap. I do have shim material but trying to wrap it around the shock stud and then slide the arm over it will just mash it up.

Thanks,

Mike