this is free, buyer pays shipping
it is a #500 back, the precursor to the 545, and 545i backs.
i have another one and use it for exposing #55 p/n and #59 film.
this is MISSING the little metal wire that at the base.
( it is what later became the little clippy thing on the 545 back )
it can easily be used to expose paper negatives
or for some sort of project