Choosing the Right Tube End Fittings

How to measure Tube Inserts, Treaded Inserts, Plastic Caps and Ferrules


Our tube fittings measurements are based on 2 key factors.

1. External Tube Diameter - Measure the EXTERNAL DIAMETER of your tube

2. Tube wall thickness - Measure  Tube wall thickness = Outside Diameter – Internal Diameter

All our range of round inserts, square tube caps and rectangular inserts are designed to fit flush with your hollow tube. Each insert has side fins that will retract to ensure a tight snug fit. For popular sizes we can offer plastic inserts to suit varying tube wall thicknesses.

Tube wall thicknesses can sometimes be described as a Gauge . The following Gauge table indicates the tube wall thickness and corresponding gauge number.

Tube Wall Thickness Gauge
0.91mm 20
1.01mm 19
1.21mm 18
1.42mm 17
1.62mm 16
1.82mm 15
2.03mm 14
2.33mm 13
2.64mm 12
2.94mm 11
3.25mm 10
3.65mm 9
4.06mm 8
4.47mm 7
4.87mm 6
5.38mm 5
5.89mm 4

So if you can measure your external tube diameter dimensions and have your tube wall thickness, we can offer you a plastic insert and plastic caps to suit your application.

The same dimensions are required for our rod and wire end tips, plastic ferrules, rubber ferrules and rubber bungs. Bolt and Nut Caps are measured on the thread diameter, which equates to a standard hexagonal head size. Threaded tube inserts measurements are the same principal as blanking plugs, which are external tube diameter and tube wall thickness.

We offer a range of imperial and metric sizes of tube fittings, so if you are unsure of your size, measure as best you can and we will offer you the nearest options for you.

If you would like a free sample of our tube fittings to test, please contact us and we would be happy to arrange this for you