These surface mounted receptacles were very popular in the 1950’s & 60’s. Believe it or not there are multitudes of these still in service throughout the US! Many row-homes used them to add a power location on solid brick walls or in hallways where access was limited. The biggest problem with them is they operate using a 16 or 18 gauge wire without grounding and are easily overloaded. Their conductors are simply extension cords tacked to baseboards or under carpeting; which are many times painted to blend in and often have damages that are exposed wiring. Their poor quality can very quickly result in fire or personal injury. If you have these or suspect you may, discontinue use and have a properly wired standard receptacle professionally installed 🔌