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How to choose caps and plugs?

clock 7 minutes | 04 Feb 2020

Range of different sized, coloured and shaped caps and plugs

The role of caps and plugs

Whether we’re talking about a fuel line, pipes, holes in sheet metal, hydraulic hose fittings or other important parts, caps and plugs play a vital role in protection, from the flexible end cap to push in plastic pipe plugs. Often the two words are used interchangeably. Caps, however, push or thread over the outside of a part, while plugs push or thread inside the part.

Caps and plugs prevent dirt, dust, moisture, liquids and any other contaminants from entering the opening during manufacturing, masking, storage and transportation. Some can be used multiple times and many are versatile enough for different stages in processes. We recommend that you try before you buy – ask us for free samples.

You need to consider your priorities before you can make your choice. The factors you should think about:

  1. Environment. This includes the possibility of dirt, debris, moisture and liquid contamination. Also what temperature will your caps and plugs be exposed to? And finally, will air or liquid pressure be involved with your application?
  2. Application. Are you looking for general protection or will you be using caps and plugs for masking or sealing?
  3. Material. Choosing the right material is critical. For instance, if using a high-temperature masking process, you’ll need a material that can perform in a high-temperature environment.
  4. Production. Process. How will the caps and plugs be applied, by hand or tool? A push fit cap or flanged plug can quickly be applied by hand. For tool-based processes, a cross head threaded plug can be used.
  5. Removal. A push fit cap or plug are not the easiest to remove. If fast removal is a priority, consider a solution with a pull tab or flange.

Here’s a closer look at the caps and plugs that suit specific needs. You can see more solutions here.

Need: Protection from damage

Tapered Cap and Tapered Plug
  1. Recommended: Tapered Cap and Tapered Plug
  2. Common uses: Storage and transportation
  3. Other reasons why:
  • Plugs multiple inner diameters
  • Caps multiple outside diameters
  • Tapered caps and plugs made of Low Density Polyethylene (LDPE), a rigid, yet soft material
Parallel Protection Plugs
  1. Recommended: Parallel Protection Plugs
  2. Common uses: Manufacturing, storage and transportation
  3. Other reasons why:
  • Resists shredding
  • Ideal for threaded applications
  • Protects against dirt, moisture and corrosion
  • Made of Low Density Polyethylene (LDPE), a rigid, yet soft material
Push-in Flange Protectors
  1. Recommended: Push-in Flange Protectors
  2. Common uses: Finishing, storage and transportation
  3. Other reasons why:
  • Flexible fins provide snug fit without the need for fasteners
  • Made of Polyethylene (PE) for high impact strength
Standard Size Pipe Caps
  1. Recommended: Standard Size Pipe Caps
  2. Common uses: Assembly, storage and transportation
  3. Other reasons why:
  • Low cost and high quality
  • Internal ribs ensure a tight fit and release after pressure build up
  • Made of Low Density Polyethylene (LDPE), a rigid, yet soft material
Cylinder Valve Cap
  1. Recommended: Cylinder Valve Cap
  2. Common uses: Storage and transportation
  3. Other reasons why:
  • Protects propane valves
  • Overfill prevention device (OPD)
  • Push fit for easy application
  • Made of Low Density Polyethylene (LDPE), a rigid, yet soft material

Need: Protection against dirt, debris, and liquid ingress

Threaded O-Ring Plugs
  1. Recommended: Threaded O-Ring Plugs
  2. Common uses: Hydraulics
  3. Other reasons why:
  • Can be applied or removed by hand, hex wrench or screwdriver
  • Compressing flange lip and O-Ring provide water tight seal for superior leakage protection
  • Available in a variety of threads
  • Available in: Polypropylene (PP) for good chemical resistance, High Density Polyethylene (HDPE) with serrated grip or Nylon for strength, abrasion resistance
Finned Stud Caps
  1. Recommended: Finned Stud Caps
  2. Common uses: Manufacturing, storage and transportation
  3. Other reasons why:
  • Protects a wide range of studs
  • Internal fins provide a strong hold and are flexible for use on various diameters
  • Comes with grip to ease removal and without grip
  • Made of Low Density Polyethylene (LDPE), a rigid, yet soft material
Quick Release Plugs
  1. Recommended: Quick Release Plugs
  2. Common uses: Hydraulics
  3. Other reasons why:
  • Designed to remain attached to hose
  • Made of Thermoplastic Elastomer (TPE) for excellent flexural fatigue resistance and high impact strength
Compression Fit Plugs
  1. Recommended: Compression Fit Plugs
  2. Common uses: Hydraulics
  3. Other reasons why:
  • Protects DKO-compression fittings not only from contaminants, but also from damage during transit and storage
  • Flexible fin provides a firm and secure fit
  • Side pull tab for easy removal
USB Dust Cover
  1. Recommended: USB Dust Cover
  2. Common uses: Electronics
  3. Other reasons why:
  • Available in different shapes and sizes
  • Made of Silicone – an excellent material for electrical insulation

Need: Easy application and removal

Pull-Tab Caps
  1. Recommended: Pull-Tab Caps
  2. Common uses: Storage and transportation – PVC / Hydraulic hoses – EVA
  3. Other reasons why:
  • Large pull tab for easy removal
  • Available in PVC for flexibility and airtight seal
  • Available in Ethylene Vinyl Acetate (EVA) for tensile strength, toughness and flexibility
Side Pull Plugs
  1. Recommended: Side Pull Plugs
  2. Common uses: Manufacturing, storage and transportation
  3. Other reasons why:
  • Protects threaded or non-threaded components
  • Pull tab feature designed for easy removal
  • Available in Thermoplastic Rubber (TPR)
  • Available in Low Density Polyethylene (LDPE)
  • Resists acid
Tear Tab Caps
  1. Recommended: Tear Tab Caps
  2. Common uses: Manufacturing, storage and transportation
  3. Other reasons why:
  • When tab is pulled, cap splits open for quick removal
  • Suitable as NPT thread plug, and UNF
  • Made of Low Density Polyethylene (LDPE) to protect from damage
Tapered Round Plugs with Flange
  1. Recommended: Tapered Round Plugs with Flange
  2. Common uses: Storage and transportation
  3. Other reasons why:
  • Excellent protection from damage, dirt, moisture and corrosion
  • Designed as both a cap and a plug
  • Wide flange keeps plug from being accidentally pushed down through the mating part
  • Flange enables easy removal
  • Tapered design can plug or cap multiple diameters
  • Made of Low Density Polyethylene (LDPE) to protect from damage
Snap Fit Plugs
  1. Recommended: Snap Fit Plugs
  2. Common uses: Manufacturing, storage and transportation
  3. Other reasons why:
  • Centre tab allows for a strong grip for easy tightening and removal
  • Suitable as a metric threaded cap, and for BSP and UNF threads
  • Made of Low Density Polyethylene (LDPE) to protect from damage

Need: End use

Sheet Metal Plugs
  1. Recommended: Sheet Metal Plugs
  2. Common uses: Automotive, specialist vehicles
  3. Other reasons why:
  • Push in plugs for panels designed to cover holes in sheet metal
  • Easy to fit with simple push and remove
  • No fastening required
  • Secure fit
  • Attractive finish
  • Made of hard, long-lasting Nylon

Round Ferrules
  1. Recommended: Round Ferrules
  2. Common uses: Automotive, specialist vehicles
  3. Other reasons why:
  • Neat cover to round-shaped tubes
  • Not just for finishing – also provides protection
  • Made of PVC for flexibility and snug fit
Secure Cover Caps
  1. Recommended: Secure Cover Caps
  2. Common uses: Furniture, outdoor equipment
  3. Other reasons why:
  • Snaps securely into place with ease
  • Conceals and protects bolt head or nut
  • Available in different colours and can be mixed and matched
  • Made of Polypropylene (PP) for good impact strength and pliability
Bolt Protection Caps
  1. Recommended: Bolt Protection Caps
  2. Common uses: Furniture, outdoor equipment
  3. Other reasons why:
  • Protects washers, bolts and nuts against weathering and tampering
  • Gives application finished appearance
  • Available with extended head for large studs
  • Protects washers, bolts and nuts against weathering and tampering
  • Gives application finished appearance
  • Available with extended head for large studs
  • Available in Polyethylene (PE) and Low Density Polyethylene (LDPE)
Banjo Union Plugs
  1. Recommended: Banjo Union Plugs
  2. Common uses: Automotive – protection of banjo unions
  3. Other reasons why:
  • Prevents dirt and moisture ingress
  • Made of Low Density Polyethylene (LDPE), a rigid, yet soft material

Need: Masking

A word about masking. Materials can make all the difference, so choose wisely according to the application you’re using. Materials react differently to processes, so before you actually start masking, just a reminder, request a free sample of the plug or masking cap for painting or for any masking process that you’re interested in. This will allow you to test it. You’ll also find masking tape convenient for areas that caps or plugs can’t cover.

Man inspecting red caps coming off a production line

If you’re looking for high temperature rubber caps, you want Silicone or Ethylene Propylene Diene Monomer (EPDM), depending on your masking process. These are both types of rubbers. You can learn more about materials in our Ultimate Guide to Caps and Plugs. Here’s a quick overview of what you need to know.

Masking: which material is best for your process?

Process Feature Powder coating E-coating Anodizing Plating Wet Painting Blasting Max Temp
Silicone Premium; reusable
+250°C
+482°F
Polyimide Tape Premium; excellent solvent
+260°C
+500°F
Silicone Tape Self bonding; perfect for irregular shapes
+204°C
+399°F
Glass Cloth Tape Durable; for blasting or thick coatings
+180°C
+356°F
EPDM Costs around 30% less than silicone
+150°C
+302°F
High-Temp Vinyl Low cost; not reusable
+170°C
+338°F
TPR Lightweight
+95°C
+203°F
Paper Low cost; recyclable
+120°C
+248°F
Polyester No shrinkage
+150°C
+302°F
High-Temp Crepe Special high-temp formula
+204°C
+399°F

We do not assume any liability for the materials, specifications or information provided. For complete temperature and other physical properties of our products’ material, please refer to the actual product material technical data sheet, available upon request.

Which solutions?

High-Temperature Silicone Tapered Plugs
  1. Recommended: High-Temperature Silicone Tapered Plugs
  2. Material: Silicone / EPDM
  3. Other reasons why:
  • Available as a solid plug or with a hollow core to aid in compression
  • Excellent chemical resistance
  • Reusable
Flexible End Caps
  1. Recommended: Flexible End Caps
  2. Material: High-temperature PVC
  3. Other reasons why:
  • Suitable for a multitude of applications
  • Flexible to ensure a tight fitting and different level of shores provides a choice in flexibility ·
Masking Washer Caps
  1. Recommended: Masking Washer Caps
  2. Material: EPDM / Silicone
  3. Other reasons why:
  • Protects threaded and non-threaded end tips
  • Washer seals the edge to protect from contaminant
Masking Pull Plugs
  1. Recommended: Masking Pull Plugs
  2. Material: Silicone / EPDM
  3. Other reasons why:
  • Masks threaded or unthreaded through holes
  • Fast, easy removal
Easy Pull Masking Caps
  1. Recommended: Easy Pull Masking Caps
  2. Material: Silicone / EPDM
  3. Other reasons why:
  • Protects end tip profiles
  • Internal seal prevents paint ingress
  • Flange provides easy removal
Masking Cone Caps and Plugs
  1. Recommended: Masking Cone Caps and Plugs
  2. Material: EPDM
  3. Other reasons why:
  • Dual role – can be used in multiple diameters
Masking Flangeless Plugs
  1. Recommended: Masking Flangeless Plugs
  2. Material: TPR / EPDM
  3. Other reasons why:
  • Masks holes without masking surrounding areas
  • Protects multiple diameters
  • Masking pull plug with tab for easy installation and removal
Polyester Tape
  1. Recommended: Polyester Tape
  2. Material: Polyester
  3. Other reasons why:
  • Masks with no shrinkage and removes cleanly in with piece after use
Polyimide Tape
  1. Recommended: Polyimide Tape
  2. Material: Polyimide
  3. Other reasons why:
  • Highly conformable
  • Excellent heat and solvent resistance
Silicone Tape
  1. Recommended: Silicone Tape
  2. Material: Silicone
  3. Other reasons why:
  • Form fitting – excellent for odd shapes
  • Waterproof seal after 24 hrs self-bonding cure
Glass Cloth Tape
  1. Recommended: Glass Cloth Tape
  2. Material: Glass cloth (Fiberglass)
  3. Other reasons why:
  • Easy to remove without fraying
  • Excellent for masking irregular shapes and corners
Crepe Masking Tape
  1. Recommended: Crepe Masking Tape
  2. Material: Crepe
  3. Other reasons why:
  • A thick pressure sensitive tape that is easy to apply and remove
  • Best for low temperature liquid and powder coatings
Paper Caps
  1. Recommended: Paper Caps
  2. Material: Paper
  3. Other reasons why:
  • Easy application
  • Environmentally friendly and economical solution

Download free CADs and try before you buy

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

Request your free samples or download free CADs now.

How to choose caps and plugs PDF download
Caps & Plugs - The Design Engineer's Guide