While I have not quite figured out all of the timelines:
Thermacote / Thermacote Co., 681 So. Raymond Ave., Pasadena, CA (420 So. San Pedro St., Los Angeles, CA 1946) / became Thermacote Welco / "Safe-T-Grip" brake spring tool, pliers manufactured by Petersen Mfg. Co., Dewitt, NE and coated with non-spark coating by Thermacote /
Thermacote Welco / Thermacote Welco, 1051 York Rd., Kings Mountain, NC 28086 (1980) (32311 Stephenson Hwy, Madison Heights, MI 48071 1978) (1313 N. Lincoln Ave., Pasadena, CA 91103) / successor to Themacote Co., Pasadena, CA, acquired by Harris Products Group 1993 /
Those various addresses shown on the packaging of those welding mask lenses were various distribution centers, not manufacturing operations. Doesn't really look like they actually manufactured any sort of "tool" other than that odd brake spring tool and those little fold-out "tip cleaner" tools used to clean welding torch tips. They did outsource a Taiwan-made pair of pliers, packaged under the "Thermacote Welco" brand name.
The subsequent mergers and acquisitions make it a bit confusing, but ultimately the company became part of Lincoln Electric Holdings Inc., the parent company of the Harris Products Group.
Discovering what patent numbers they were issued, or any trademarks (if such exist) might help establish timelines on their various locations.
