A guide to tube inserts

Round plastic tube inserts used on furniture legs

Exactly what is a tube insert?

This guide is designed to answer your questions, and covers the topics:

Tube inserts are small components sometimes called box section caps and are either designed with ribs or a straight wall. They can serve several functions:

1. Finish off tubes, posts, boxes or pipes

Tube insert diagram

Plastic tube inserts are commonly used to enhance the appearance of applications. They’re popular for furniture, such as feet for office and school chairs, desks and workstations. They’re also put to use on light-duty machinery. You’ll find them in consumer products, too, such as tripods. As feet, they grip the floor while protecting floors from damage.

2. Protect assemblies against ingress and sharp edges

Some threaded tube inserts are designed to protect assemblies from a tube’s sharp edges while still providing an aesthetic appearance. Tube inserts are also ideal for prevent dirt and moisture ingress to protect your application and prolong its life. Depending on the material, tube inserts can be used outside to cap off posts to prevent oxidation and reduce maintenance costs.

Tube inserts and glides

Tube inserts and glides

Glides are used on the bottom of furniture legs to protect the floor from damage. They’re sometimes called glide inserts. Some have adhesive backs that stick onto furniture legs, while others are nailed on or screwed in.

Glides fit into a tube to reduce friction and dampen noise. When a tube insert is used on the bottom of furniture feet – or as feet themselves – you’ll usually find a glide is part of the tube insert’s design.

Types of tube inserts

Tube inserts and tube insert glides are available with different features. Some are ideal for attaching leveling feet or casters to. You can learn more about feet in our Guide to leveling feet.

​Square tube inserts – angled

Square tube inserts – angled

  • Unthreaded square tube ends
  • Ideal for uneven surfaces, applications with fixed leg angles, or when tubes meet surfaces at an angle
  • Push fit for easy insertion
  • Ribbed to aid insertion and retention
  • LDPE
​Threaded rectangular ribbed tube inserts

Threaded rectangular ribbed tube inserts

  • Metal internal threads accommodate adjustable leveling feet
  • Ribbed design suits multiple tube gauges
  • High head and flexible ribs ensure secure fit
  • HDPE
​Round tube inserts

Round tube inserts

  • Chrome capped
  • Threaded center
  • Push fit for easy insertion
  • LDPE
  • Steel base also available
​Rectangular tube inserts

Rectangular tube inserts

  • Ribbed or straight-wall design
  • Protects sharp edge of metal tubes
  • Polished finish provides aesthetic appeal
  • Also available in eroded and textured finishes
  • LDPE or ABS, in different colors
​Threaded round tube inserts

Threaded round tube inserts

  • Threaded inserts accommodate adjustable leveling mounts and feet
  • Threaded brass insert for indoor and outdoor applications
  • Push fit
  • Different styles available
  • Glass-filled nylon. Also available in zinc-plated steel and HDPE
​Threaded square tube inserts

Threaded square tube inserts

  • Protects assemblies from share edge of the tube
  • Internal thread accommodates leveling feet, tilt glides or castors
  • Enhances aesthetics
  • Push fit
  • Zinc-plated steel, nylon or HDPE
​Domed square inserts

Domed square inserts

  • Ideal for applications with variable leg angles
  • Square rocker glides fit flush with tubing outer dimensions to present a clean, finished look
  • Push fit
  • ABS


Tube inserts and glides are manufactured in both plastics and metal. Popular metal tube inserts include steel and aluminum. Steel and aluminum are good choices for heavy-duty applications, when structural integrity is paramount. Both aluminum and steel tube inserts do an excellent job of resisting compression. Also available are plastic tube varieties with metal thread inserts, such as brass, or plastic inserts.

Plastics offer more variety. You can formulate any plastic to bring out the characteristics you want. For instance, nylon on its own does not stand up well to UV rays in the long term, but additives can strengthen this ability. Plastic box sections, or tube inserts, are easily available. To decide which plastic tube insert is best for you, start with comparing materials:




GF nylon




Electrical insulation





Good –Excellent

Good –Excellent

Acids & alkalis resistance





Very good

Very good

Aromatic hydrocarbons resistance







Dimensional stability




Good (with annealing)


Poor – fair

Tensile strength





Fair – good

Very good

Impact resistance







Heat resistance

Good (with additives)

Good (excellent with additives)

Very good

Good (with additives)



Industrial tube inserts

Measuring for the correct tube-insert size

To get the perfect fit, follow these steps for measuring for tube inserts, whether round, square, rectangular or oval.

Step 1 - OD: Find the outside diameter of the tube (OD) by measuring the distance between the outer lips, or end to end.

Outside diameter

Step 2 - ID: Find the inside diameter (ID) of the tube by measuring the distance between the inner lips.

Inside diameter

Step 3 - Wall thickness: Wall thickness is also known as the tube gauge. You can either use a tube-thickness caliper to measure the wall thickness as shown below or use the formula: OD-ID ÷ 2.

Wall thickness

Step 4 - Matching the tube to the tube insert: When using a tube-thickness caliper to measure wall thickness, you’ll get a round figure. Popular gauges range from 10 to 20. Using the formula gives you your wall thickness in inches or millimeters.

Using our square angled tube inserts as an example, you can see how to read what size tube insert you need. In the table below, you’re given both the tube gauge and the wall thickness, in case you used the formula.

Tube sizing

The lower the gauge number, the thicker the tube’s wall thickness. Generally, the rule of thumb for gauge and wall thickness works out like this, but there will always be slight variances:




























square domed inserts.

Using outside diameter and tube gauge to choose your tube insert

As an example, let’s look at our square domed inserts. Online, these are grouped by the size of the tube you need the insert for, with the gauge. By size, we mean the tube’s outside diameter. If you only know the outside diameter of your tube, find the size in the left hand column, as in the example below. The righthand column tells you the gauge that’s compatible with your tube.

Square domed insert sizing

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 make sure you’ve chosen exactly what you need. If you’re not quite sure which solution will work best for your application, 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.


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.