Stimpson offers several styles of hole plugs: standard, electrical knockout, tubing.  Plugs may come in a variety of materials, including steel, carbon steel, brass, and stainless steel.  Most are made in one material only, but a few may be available in two or more.

Steel, carbon steel and brass hole plugs can be plated with zinc, nickel or other finishes for the purposes of corrosion protection and/or appearance.

Our Standard plugs are round and have several prongs that are designed to snap into a specific size hole and remain in the hole unless a significant amount of force is applied to pry them out.  Each plug has a designation for “Hole Size” which is very different from the hole size dimension used for eyelets and grommets. When used in the context of hole plugs, it is the size of the hole into which the plug is expected to fit.  The prongs of each standard hole plug are slightly bent so that the widest part of the prong holds the plug firmly against the back of the material.  Therefore, each hole plug indicates a “thickness of work” through which it can be expected to snap into and hold firmly.

If a customer’s material has a thickness of 1/16”, for example, a hole plug that is designed to grip 1/16″ thick material is required.  If the material is thinner than what is indicated as the “thickness of work”, the plug may sit loosely in the hole and be relatively easy to remove.  When thicker, the plug’s prongs may not pass through the material completely enough to allow the prongs to grip, and the plug may fall out of the hole unintentionally.  Blueprints also designate the diameter and height of the head of each plug (the part visible above the surface of the material), and the overall length of the plug.  Users should make sure that the head and the prongs have clearance in the application.

Electrical Knockout plugs are generally to be used in electrical boxes to close unused holes.  In the event of a short in the wiring, the plug will prevent sparks from exiting the electrical box and possibly causing a fire.  Knockout plugs also prevent vermin and contaminants from entering the electrical box and causing failures.


These plugs are sized by industry standard knockout sizes.  It is important to note that these standard sizes are NOT exact hole sizes.  Similar to our standard  plugs, the prongs of these plugs are configured so that the bend of each prong grips the inside of the electrical box for a tight fit.  The prongs can be bent outward (manually) for additional grip, but the plugs should remain securely attached regardless as long as they are inserted in the correct size hole.

Tubing hole plugs work differently than standard plugs.  As these plugs are designed to fit in the end of a tube, the prongs generally cannot pass all the way through and grip the back.  Instead, they remain in place by friction.  Like other plugs, the prongs are bent  slightly, and the widest part of the prongs is usually a bit wider than the tube into which they are intended to fit.  When inserted, the friction between the widest part of the prongs and the inside of the tube allows the plug to remain in place.  For each plug, an inside and outside diameter of the tube is specified.  This ensures that the plug will fit snugly in your tube, and also will cover its end completely.  The diameter and height of the head (the only visible part after insertion) are also indicated, as well as the overall length.