Overview
- The holes let small spring clips inside many wall outlets catch the blades and hold the plug in place.
- A tighter grip keeps the flow of power steady and lowers the risk of sparks, heat buildup, shorts, and slip‑outs.
- NEMA rules set common North American plug types, with Type A using two flat blades and Type B adding a ground pin for extra safety.
- Using low‑quality adapters that lack this retention feature can raise the chance of arcing and fires, according to the reports.
- Engineers trace the perforated‑prong design to Harvey Hubbell II’s 1904 detachable plug, which later informed standard practice.