Here's a period ad for it:
http://books.google.com/books?id=7UofAQAAMAAJ&pg=PA280&lpg=PA280&dq=Hoover+Rim+R emover+instructions&source=bl&ots=wFDh4IAOEq&sig=OqB4D2_igbR_s41bWH5EuPs6dbE&hl= en&sa=X&ei=XaoJVPK_JcS0yASt5YLgBQ&ved=0CCwQ6AEwAA#v=onepage&q&f=false
I finally figured out how to extract the ad picture from the Google book page. It looks like the tool helps to remove stubborn demountable rims that have rusted or otherwise stuck to their felloe.
Thank you.