I have two cap hooping hoops that attach to brother, babylock, and possibly other embroidery hoops.
I received these as part of the set when I ordered extra hoops for my machines. I have no interest in embroidering caps.
They clamp onto your current hoop, and you stick the brim of the cap into the attached clip, on top of your sticky stabilizer. They can be purchased separately, or together. they are listed for $20 each.
They come from a smoke free home with pets present.
They can be picked up locally, or shipped if you pay shipping.