The anti-magnetic Ajax Insulators sold by the Newark Watch Case Company typically featured a glossy black exterior and soft lining to protect the watch.
The most common variant was the option with an opening cutaway for the watch dial. However, insulators were also available that completely encased the watch, requiring the owner to open the Ajax Insulator to look at the dial.
The original box included a guarantee by the company:
“We hereby guarantee that the enclosed Insulator protects the WATCH CASE from wear, and the WATCH from all ordinary magnetic influences.”