Screw & Bar Knockout Seals

Available in multiple trade sizes ranging from 1/2” through 4”, our selection of screw & bar knockout plugs is ideal for commercial, industrial, and residential electrical installations.

• Strong steel construction
• Secure screw & bar locking mechanism
• Trade sizes from 1/2” to 4”
• Ideal for panels, junction boxes & enclosures
• Professional, code-compliant finish

What Is a Screw & Bar Knockout Seal?

A screw and bar knockout seal is used to close an unused knockout hole in an electrical box or panelboard. When a knockout has been removed but is no longer needed for conduit entry, the opening must be properly sealed to maintain enclosure integrity and meet electrical code requirements.

Unlike snap-in knockout plugs, screw & bar seals use a metal backing bar and machine screw to clamp tightly against the enclosure wall. This creates a more secure and vibration-resistant installation—especially important in commercial and industrial environments.

Where Are Knockout Seals Used?

Knockout seals are commonly installed in:

• Steel junction boxes
• Load centers and breaker panels
• Metal enclosures and cabinets
• Commercial electrical raceway systems
• Industrial control panels

If a knockout opening remains exposed, it can allow dust, debris, pests, or accidental contact with energized components. Installing the proper size knockout seal restores the enclosure to a safe and professional condition.

Available Trade Sizes

We offer screw and bar type knockout plugs in the following trade sizes:

• 1/2 Inch
• 3/4 Inch
• 1 Inch
• 1-1/4 Inch
• 1-1/2 Inch
• 2 Inch
• 2-1/2 Inch
• 3 Inch
• 3-1/2 Inch
• 4 Inch

Always match the seal size to the original knockout trade size—not the measured hole diameter. Trade sizing corresponds to conduit size standards.

Why Choose Screw & Bar Style Over Snap-In Plugs?

• More Secure Fit: Mechanical tightening provides a firm hold.
• Better for Vibration Areas: Ideal in industrial settings.
• Larger Sizes Available: Commonly used for 2” and larger openings.
• Professional Appearance: Clean, flush exterior finish.

For larger knockout openings (2” and above), screw & bar designs are typically preferred because snap-in plugs may not provide sufficient holding strength.

Material & Construction

Most screw & bar knockout seals are constructed from plated steel for durability and corrosion resistance in standard indoor applications. They are designed for use in dry locations unless otherwise specified by the manufacturer.

For specialized environments, always confirm material specifications and ratings for your specific application.

Code Compliance & Safety

Electrical codes require unused openings in boxes and cabinets to be effectively closed. Properly installed knockout seals help maintain enclosure safety standards and reduce risk of exposure to energized components.

Whether you are completing a new installation or modifying an existing electrical system, installing the correct knockout seal ensures your work meets professional standards.

Multiple Brands Available

At Brand Name Lighting, we offer screw & bar knockout seals from leading electrical manufacturers. As our catalog continues to grow, additional brands and configurations will be added to provide more options for contractors, electricians, and facility maintenance professionals.

Need help selecting the correct size?

If you’re unsure which knockout seal you need, our team is happy to help. Contact us with your box type and knockout size, and we’ll guide you to the right solution.