Caps, Grips, and Closures Selection Guide Caps, Grips, and Closures Selection Guide Caps, Grips, and Closures Selection Guide

Image Credits: Alliance Plastics | LADD Industries, Inc. | Newark / element14

 

  

Grips, caps, and closures are used to protect the end of a shaft, tube, pipe, bottle, screw, bar, or other item during shipping, storage, masking, or other applications. Some caps can also be used to provide a hand grip or hanger tip.

 

Type

 

The most important factor in grip, cap, and closure selection is the type. Type is defined either by the shape of the cap or the means by which the cap is fitted.

 

Shape Type

 

Type

Description

Example

Round-shaped

Round or circular shaped caps and plugs have circular dimensions and are meant to fit onto objects with round ends, such as bottles or circular tubes.

Caps, Grips, and Closures Selection Guide

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Square-shaped

Square shaped caps and plugs have equal length and width dimensions and are meant to fit onto objects with square ends.

Caps, Grips, and Closures Selection Guide

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Rectangular-shaped

Rectangular shaped caps and plugs have varying length and width dimensions and are meant to fit onto objects with rectangular ends.

Caps, Grips, and Closures Selection Guide

Image Credit: LADD Industries, Inc.

Hand grips

Hand grips are caps used specifically as handles or grips. They may have finger nubs for easier gripping.

  • Round handles have circular cross sections.
  • Flat grips have square or rectangular cross sections.

Caps, Grips, and Closures Selection Guide

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Hex caps

Hex caps are hex-shaped for use with hex stock, nuts, and fittings.

Caps, Grips, and Closures Selection Guide

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Screw caps

Screw caps or plugs are specifically designed for covering a screw or screw socket.

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Washer caps

Washer caps have holes in the center and are used between tubes or hoses and end fittings.

Caps, Grips, and Enclosures Selection Guide

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Connection Type

 

Grips, caps, and closures are designed with one of three connection methods.

 

  • Push-fit caps and plugs connect to ends simply by applying downward pressure. These closures typically provide a tight fit, but are easy to remove.
  • Caps, Grips, and Closures Selection Guide

 

 

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  • Tapered caps and plugs are connectors with tapered sides, providing a snug fit. Some can be used as either a cap or a plug. Tapered caps and plugs are versatile and can be used for straight tubes and bars, male and female NPT threads, and male straight threads.

    Caps, Grips, and Closures Selection Guide

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  • Threaded caps and plugs have threads designed to attach to threaded ends of pipes, tubes, and other forms. Caps have female threads and plugs have male threads. Some threaded caps may incorporate a quick-twist style with a clip or lock that engages the cap in place.

    Caps, Grips, and Closures Selection Guide

 

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Sizing Specifications

 

Cap dimensions must be matched and selected according to the object they are covering or protecting. Sizing specifications will vary based on the shape of the cap.

 

Circular Dimensions

 

These dimensions only apply to round caps.

 

  • Diameter is a dimension expressing the cross sectional distance spanning across the cap circumference. Caps should be sized in order to fit the diameter of the round objects they are capping or covering.
  • BSP sizing applies to caps designed to fit objects with male BSP (British Standard Pipe) threading.
  • NPT sizing is used for closures designed to cap objects with male NPT (National Pipe Thread) threads.

Square or Rectangular Dimensions

 

These dimensions only apply to square or rectangular caps.

 

  • Length is the larger cross sectional dimension for rectangular caps. If the section is a square, the width and length are the same dimension.
  • Width is the smaller cross sectional dimension for rectangular caps. If the section is a square, the width and length are the same dimension.

Material

 

It is also important to consider the material of the grip, cap, or closure. Material typically dictates the physical properties of the cap; most importantly its hardness, flexibility, and resistance to wear or degradation. Additionally, it is often important for the material to match that of the item being protected or covered.

 

Caps, Grips, and Closures Selection GuideMetals

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  • Aluminum is a very versatile metal that is lightweight, strong, durable, flexible, impermeable, corrosion-resistant, and recyclable.
  • Stainless steel is a steel alloy containing over 10.5% chromium. It is used in applications where excellent corrosion resistance and high strength are required.

PlasticsCaps, Grips, and Closures Selection Guide

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  • Ethyl vinyl acetate (EVA) is a transparent thermoplastic elastomer. It remains flexible at low temperatures and resists cracking. Brand names include: Ultrathene® (Quantum), Elvax® (DuPont), Evalca® (Eval).
  • Nylon, comprising several grades of polyamides, is a general purpose material in wide use; it is tough and resistant and has good pressure ratings and mechanical strength for its cost.
  • Polyethylene (PE) comes in high density (HD) and low density (LD) forms. The high density form is a high strength, rigid plastic with temperature resistance up to 215°F. The low density form is a flexible, semi-rigid plastic with a temperature resistance up to 175°F. Low density polyethylene is the most common material used for manufacturing caps and plugs.
  • Polypropylene (PP) is a high strength, rigid thermoplastic material exhibiting excellent cold flow, bi-axial strength, and yield elongation properties. It is similar to PVC but can be used in exposed applications because of its resistance to UV, weathering, and ozone. It resists temperatures up to 250°F.
  • Vinyl exhibits good flexibility and chemical resistance; it is used in many medical and chemical applications. Its properties can be enhanced or modified by compounding it with additives or modifiers to meet different application needs.

Caps, Grips, and Enclosures Selection GuideOther

 

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  • Paper caps are considered more environmentally friendly than plastics and metals and are typically 100% recyclable. They are frequently used for high-temperature applications that may degrade plastic caps or plugs. Because paper is hygroscopic, excessive humidity changes or water contact can cause dimensional variation or warping.
  • Silicone rubber is made from cross-linked silicone based polymers reinforced with filler. Silicone rubber is very resilient, and boasts long service life through adverse environments. The operating temperature range for silicone rubber is wide, from -148°F to 600°F.

Features

  

Caps, grips, and closures may incorporate a number of features into their design which may be important for certain applications.

 

  • Hanger tips allow for the hanging of tools or other items. They are sometimes integrated with handles or grips.

Caps, Grips, and Closures Selection Guide

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  • Lift/pull tabs and rings allow caps to be easily removed. Pull plugs are designed for "through-hole" applications.  They use a smaller diameter "pull section" to pull the plug until it is snug in the hole.

Caps, Grips, and Closures Selection Guide

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  • Tear tabs are inserts which can be pulled for easy cap removal. When the tab is pulled, the cap tears away. Once removed, the cap cannot be reused.

Caps, Grips, and Closures Selection Guide

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  • Vented caps are commonly used in the medical industry. The vent allows air flow during gas sterilization and prevents the cap from blowing off during extreme heat conditions.

Some features are specific to round-shaped caps.

 

  • Anti-roll caps are round caps with a square end to prevent tube or shaft from rolling.

Caps, Grips, and Closures Selection Guide

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  • Flange caps have flange edges included for easily removal or additional protection of the bearing surface. They also prevent accidentally pushing the plug all the way through the opening.

Caps, Grips, and Closures Selection Guide

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  • Knurled or faceted heads have perforations on the outside of the cap, allowing easier installation and removal, either by finger or wrench.

Caps, Grips, and Closures Selection Guide

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  • Slotted heads have a slot to allow the cap to be installed or removed with a screwdriver.

Caps, Grips, and Closures Selection Guide

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References

 

Select Caps and Plugs by Material Type - Caplugs


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