Thanks, Miriam. The seller said he was an "old singer nerd", so I emailed him to ask if it was all metal inside. He replied and said it was a mix of nylon and metal gears. I'm gonna wait until an all metal free arm comes along. But I went to the guy's website and was pretty impressed with the stuff he makes. I really like the waxed cotton bags and packs.
http://www.tombonamici.com/soft-goods