I picked up this Dasco cold steel wood chisel.  It is 8 1/2 inches long and weighs 8 ounces. I like the design of the tool.

I've seen those solid steel wood chisels described sometimes as "plumber's chisels," plumbers apparently being considered too brutal for regular wood chisels.  It is a nice design.

Plumber's Chisels?  Neat description.   Dasco appears to have made two sets.  A straight set like this chisel (36x series) and an angled set (46x series).  Standard 4 chisels on each, 1/4. 1/2, 3/4, an 1 inch.  There may have been larger sizes.  Craftsman also made a set as did  Mayhew.

A plumber is generally not carving acanthus leaves as part of his job.
He DOES however have to chop through a floorboard or stud to run a pipe.
Sometimes a saw or a drill won't work.

True.  And whacking out a suitable opening in old framing ain't easy.

That probably explains why holes around retrofitted pipes in tight spaces in older houses tend to be more squared off than round?   Easier and cheaper to carry a chisel than a corner brace.