Here's some information on the company preprinted on the Reply Card, the Wilcox Manufacturing Company of Aurora, Illinois:

Considering its slogan
"A Hangar for Any Door that Slides" one wouldn't think they'd still be in business, but believe it or not, they still are (and at the same location!) but their core business has expanded into the following:
Quote:
From the early door hangers, the product line progressed to engineered systems for folding partitions and doors for school gymnasiums, as well as continuous power conveyor overhead track systems for other manufacturing processes and even systems for transporting crippled children in swimming pools for health and recreational purposes.
Richards-Wilcox, Inc., located in Aurora, Illinois, is a privately owned manufacturer of office storage and filing systems, overhead power and free conveyor systems, and door hardware. The company, founded in 1880, has been in continuous operation at the same location.
Our office products, branded under the Aurora name, include Quik-Lok® Shelving; high density manual and electric Mobile Systems; Times-2 Speed Files®, a double-sided rotating file cabinet; and Wood-Tek™, a line of premium wood-clad case goods.
Richards-Wilcox overhead conveyor systems are available as manual or powered models. Safe-Rail®, Zig-Zag®, Twin-Trak® and Over-Way™ are industry standards for moving material efficiently and safely.
Richards-Wilcox Door Hardware products are used in a variety of markets including zoos, aquariums, barns, stables and commercial and residential historic applications.