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Hole plugs, explained

clock 7 minutes | 24 Jun 2022

Pile of brightly colored hole plugs

What are hole plugs?

All plugs fill holes, but not all holes are the same. Some are intended while others are accidental. Whatever the case, holes need to be sealed to prevent dirt, dust and moisture ingress. Covering the holes not only provides a clean finish, but also helps achieve structural integrity. This is the job of a hole plug, which is typically a push plug.

In this guide, we’ll explain what hole plugs are and cover these elements:

Plugs for holes come in different types for different functions. Some push-in hole plugs seal chassis holes and wiring outlets. Others are designed as screw-hole plugs, typically made of wood. Still others close off access holes. Hole plugs can top tube ends, or even act as protective bumpers, small appliance feet and drawer glides.

You can also get square, rectangular and round hole plugs in different materials.

What are bungs?

These are typically stoppers used to seal tubes and bottles. Often made of rubber, some have holes which enable scientists to connect different flasks with tubes. Most rubber plugs, or bungs, are tapered, though some are straight edged. Plastic bungs are also common. The plastic bung shown here is made of LDPE and is pushed into fabricated bores to provide protection and aesthetics.

Plastic bungs

Types of hole plugs

We’ll first look at plugs designed to prevent ingress of dirt, dust and moisture ingress.

​Finned hole plugs

Finned hole plugs

  • Ideal for sealing thin-walled copper tubes
  • Quick to fit
  • Features a small pull-tab for easy removal
  • Flange prevents plugs from being pushed into tubes
  • LDPE
​Parallel protection plugs

Parallel protection plugs

Available in:

  • TPR – ideal for protecting connectors and providing a clean finish in electronic applications; stands up to acids
  • LDPE – perfect for protecting pipes, tubes, valves and flanges from damage and ingress during transport and storage
  • PVC – highly resistant to shredding
  • Vinyl – suited for applications where oils and grease are present
​Barrel plugs

Barrel plugs

  • Barrel shape for snug fit forms a tight seal
  • Push fit for easy insertion
  • Flange for easy removal
Banjo union plugs

Banjo union plugs

  • Typically used by automotive industry
  • Used to protect banjo unions
  • Flexible LDPE for snug fit
​Push-in plugs for SAE & NPT threads

Push-in plugs for SAE & NPT threads

  • Threaded hole plugs
  • Tapered design allows each part to plug multiple diameters
  • Designed for plug SAE & NPT tapered threaded fittings
  • LDPE
​Tube end plugs

Tube end plugs

  • Effective sealing
  • Ideal for postal tubes, composite containers and for plugging plastic tubing
  • Available with finger grips for easy insertion and removal
  • LDPE

Panel plugs

Plugs for holes in metal are typically designed for closing panel cavities while providing protection from sharp edges. Push-in panel plugs also protect against dust, dirt and moisture ingress during cleaning and manufacturing processes.

​Blanking plugs

Blanking plugs

  • Provides a neat, finished appearance
  • Available in different shapes
  • Available in silicone, rated IP 67, with a pull tab for easy grip and removal
  • Also comes in nylon, PVC and TPR
​Body plugs

Body plugs

  • Each size fits a range of panel thicknesses
  • Available in TPE, rated IP 67 – resists oils, acids and alkalies
  • Also comes in TPR and silicone for withstanding high temperatures
​Sheet metal plugs

Sheet metal plugs

  • Similar to button plugs, providing a decorative finish
  • Quickly snaps into place
  • Ensures a secure fit for entry holes
  • Nylon 6/6
​Vented locking plugs

Vented locking plugs

  • Excellent wire hole plugs, closing wiring or production access holes
  • Vents allow heat and emissions to escape
  • Nylon 6/6
Hole plug industrial setting

Plastic hole plugs: materials

Metal-hole plugs often refer to the plugs used to fill holes in sheet metal. The plug is usually plastic, although hole plugs can be made of metal. Metal plugs for holes are not commonly used but when they are, it’s usually to achieve an aesthetic effect.

Plastic plugs for holes are popular for their ease and flexibility for snapping into threaded and non-threaded holes. They’re also easy to remove. Rubber hole plugs are another option. Often rubber is referred to thermoplastic rubber, or TPR. TPR looks, feels and performs very much like rubber, but costs less.

Similar to TPR is thermoplastic elastomer, known as TPE. It’s often difficult to tell the two apart, but as a general rule of thumb, TPR is harder than TPE. TPE also costs less. Silicone and PVC are yet other similar materials, often used for masking processes. You can see how they all compare here:

Comparing materials

Resistance to chemicals TPE TPR PVC Silicone
Acids 3 4 2 2
Bases 3 4 3 2
Hydrocarbons 1 2 1 2
Sea water 4 4 4 4
Water 4 4 4 4
Max. operating temperature 210˚F
275˚F 200˚F 446˚F
Typical cost $$$ $$$$ $$ $$$$$


1=Poor/ 2=Fair / 3=Good / 4=Very good

LDPE and nylon 6/6 are two of the most popular materials when it comes to plastic plugs for holes in metal – or in any material, really. These two plastics are primarily used for plugs that protect against damage and ingress.

Resistance to chemicals Nylon 6/6 LDPE
Dilute acids 1 4
Dilute alkalis 2 4
Oils and greases 4 2 (variable)
Aromatic hydrocarbons
4 1
Halogenated hydrocarbons
3 (variable) 1
Alcohols
1
4

1=Poor/ 2=Fair / 3=Good / 4=Very good


LDPE, nylon and silicone are thermoplastics. You can learn more about these materials in Thermoplastics for caps and plugs.

Plastic plug holes: sizes

If your plug is intended to fill a panel hole, you’ll need to take two measurements:

1. The outside diameter of the hole, as shown here

2. The thickness of the panel

Hole plug diameter

You then match your measurements to the plug manufacturer’s size chart. If your hole’s outside diameter measures 0.625 inches, then ¾ inch plastic hole plugs will be appropriate for a snug fit.

Let’s say you want to use a domed blanking plug. Essentra Components makes it easy to select the size that you need. Let’s say your hole measures just over 0.8 inches. Note the compatible hole diameter. It matches your hole measurement. As you see in this portion of the specifications, a 1-inch hole plug will suit your needs.

Hole plug dimensions

Notice that the specifications also include height, or length. Go back to your measurement for panel thickness. If the length of this plastic hole plug does not exceed the dimension given here, then this is the perfect size for you.

You also have the option to view the sizes in millimeters for metric hole plugs.

Download free CADs and try before you buy

Free CADs are available for most solutions, which you can download. You can also request free samples to ensure the hole plug you’ve chosen is exactly what you need. If you’re not quite sure which product will work best our experts are always happy to advise you.

Whatever your requirements, you can depend on fast despatch. Request your free samples or download free CADs now.

Questions?

Email us at sales@essentracomponents.com or speak to one of our experts for further information on the ideal solution for your application 800-847-0486.

Hole plugs