Bingo - I got a hit! A plumbing warehouse in Cleveland Ohio has been around since 1933, so, I took a shot hoping somebody from there might know something about Covers company in Bedford (a suburb).
http://www.lakesidesupply.comHere's their reply to my email:
Thank you for your inquiry.
We have some basic information on the Covers Co. and have a few tools from the company in the museum. Covers Co. was started in the 1930s by Harold and Helen Maguire. The first products were metal and rubber plug for leaks in hot water tanks and boilers. They also covers for vehicle radiators and that is how the company got its name. They also made plumbing tools and were known for the Covers wrench. While it had been in business for many years, Covers Co. was not incorporated until 1961. Following the founder's death in 1968, management of the company was taken over by the family. The business closed in 1996.
