Hi!
We sent out our packet today and we DID use binder clips, 2 in fact , as ours was also very thick. I saw someone mention the USCIS suggests not to use binder clips. I went through the link:
https://www.uscis.gov/forms/filing-guidance/tips-for-filing-forms-by-mail
and read this:
”Do not use heavy-duty staples. Instead, use fasteners or heavy clips to hold together thick or bulky applications or petitions.”
So I think clips are ok. Just not binders.