Electrical Box Knockout Plugs

Electrical box knockout plugs seal unused openings in junction boxes, electrical panels, and conduit bodies, keeping installations safe, code-compliant, and tidy. By closing open knockouts, these KO seals block dust, debris, and moisture, help preserve fire-resistance and enclosure ratings, and deter pests. They also reduce unintended air leakage in conditioned spaces and protect conductors from accidental contact.

Choose from snap-in knockout plugs for fast, tool-free installs or screw-tight and threaded knockout seals for vibration-prone or outdoor environments. Materials include zinc-plated steel for strength and grounding continuity, stainless steel for corrosion resistance, and durable nylon or PVC for nonmetallic boxes. Gasketed, weatherproof knockout plugs help maintain NEMA 3R or 4X performance in wet locations. Most sizes match common trade diameters—1/2 in., 3/4 in., 1 in., and larger—to fit standard box knockouts. Look for UL listed, CSA certified, and NEC compliant options to satisfy inspectors.

Selection tips:
- Match the trade size to the knockout, not the conduit O.D.
- Align material and finish with the box type and environment.
- Use gasketed or watertight plugs for outdoor or washdown areas.
- Choose low-profile or tamper-resistant styles for clean aesthetics and security.
- Keep a mixed assortment on hand to speed service calls.

Installation is simple: remove burrs, press or tighten the plug until seated, and verify the seal sits flush without distorting the box. For metal boxes, confirm bonding where required; for plastic boxes, avoid over-tightening.

Whether you are finishing new work or correcting an inspection punch list, electrical box knockout plugs offer a neat, reliable way to close unused holes. Browse steel knockout plugs, snap-in hole plugs, and weatherproof knockout seals to keep junction boxes and electrical panels protected, compliant, and professional. Find trade-size knockout plugs for metal and nonmetallic enclosures, replacement KO seals for remodels, and UL listed hole plugs for fast electrical repair.