I found a lightly rusted, not uncommon IHC wrench (at top, in picture below) with a loop handle being offered among the snowbanks at the local flea market a week ago. After cleaning it up, it was compared with another single-shaft handled IHC wrench I obtained several years ago. Both wrench heads are stamped "5 E", and both wrenches are 11 5/8" in length. The top wrench is embossed "7 1/2 E" on its handle, while the bottom wrench is embossed "7 E" on its handle.
I would like to know more about the equipment these wrenches were assigned to, and what period they were made in. It's my belief that these wrenches are still fairly common, at least they were 10 years ago.