I just picked up one of these mini Prentiss vises.
I got it at an antique shop and it had a few coats of paint on it.
I stripped it all off with oven cleaner, degreaser, then naval jelly and finally some oil.
I think it's looking pretty good!
After its cleaning and oiling, this thing is smooooth.
The only markings are the patent date on the spring loaded swivel pin and an inspector stamp (#20) under the jaw.
I can't get the rear jaw swivel pin loose. I might try to heat it up with a mini torch and pull it out. I would like to see that rear jaw move!
I can't find any info on this thing online. I really wish I knew more about it.
The closest I can find is one in this thread from 1FordTech1, but his doesn't have the rear swivel jaw.
http://scuttle.dayid.org/wiki/index.php/Prentiss_Vise (See the bottom photo)
I'll see if the admin of that site will add my photo for reference.