How to measure a profile or tube to find the right size end cap

The type of tube or profile measured

Hollow profile or tube

Hollow profiles or tubes are generally made of steel, aluminum, or stainless steel with wall thicknesses of a few millimeters. For these hollow profiles (such as those used for chair or table legs), it is essential to measure BOTH the outer dimensions AND the inner dimensions. Obviously, the outer dimensions are always larger than the inner dimensions. However, two hollow profiles can have the same outer dimensions (e.g., a 25mm diameter) but different inner dimensions (20mm for one and 18mm for the other) due to a different wall thickness.

Hollow profiles or tubes can accommodate either inserts (plugs that go inside) or caps that cover the tube. For inserts, measuring the inner dimensions is an important step to ensure that the insert will hold firmly enough within the tube. The deformation of the fins on the inserts provides this function and guarantees that the insert will stay securely in the tube. For external caps, we only consider the outer dimensions of the tube to choose the appropriate cap.

Solid profile or tube

Solid tubes or profiles can be made of metal or wood. For dimensioning, only the outer dimensions are possible and useful for choosing the appropriate cap. For these solid tubes, external caps are the only solution. These external caps are designed such that their shape ensures sufficient pressure on the outside of the tube to stay in place. The choice of the appropriate cap will be based on the outer dimensions mentioned on the cap’s product page. These must be similar to the dimensions of the profile on which it will be installed.

Taking measurements according to the shape of the tube or profile

How to measure correctly?

To effectively measure the dimensions of a profile or tube, whether round, square, or rectangular, we recommend using a caliper. This instrument will give you an accurate measurement of the outer dimensions and will allow you to measure the inner dimensions easily. A ruler or tape measure can also be used for measurement, but be very careful when taking the measurement to be well-aligned or to take precise reference points.

The measurement stage is the critical moment during which your full attention must be focused. Taking accurate measurements guarantees that you will choose the perfectly adapted insert or cap.

Taking measurements of a round tube

Taking measurements of a hollow round tube is done in two steps: the Outer diameter and the Inner diameter

In our range of inserts, choose the insert with the Outer diameter that corresponds exactly to the Outer diameter measured on your tube. Thus, the insert will be perfectly flush with the tube (no protrusion or recession), which ensures an ideal aesthetic for your tables, chairs, etc., perfect protection, and optimal service life. This last point is particularly true for a tube leg insert, on which significant forces are applied. Indeed, by being flush, the weight and forces are distributed ideally on the insert according to the installation conditions considered during its design.

Once you have found the insert(s) whose Outer diameter matches that of your tube, ensure that the Inner diameter of your tube is within the range of Inner diameters mentioned on the insert’s product page.

For example, for a tube with a measured Inner diameter of 18mm, choose an insert with an Inner diameter of 17-19mm, 18-20mm, or 16-18mm. Your tube’s inner diameter must be within this range to guarantee a perfect fit.

In our range of external caps, choose the cap with the Outer diameter that corresponds exactly to the Outer diameter measured on your tube. The cap will cover your tube with a calculated pressure to stay perfectly in position and resist use-related stresses (chair legs, table or desk legs) over time.

Taking measurements of a solid round tube requires measuring the Outer diameter

For a solid round tube, only external caps can be used. As in the previous case, choose the cap with the Outer diameter that corresponds exactly to the Outer diameter measured on your solid tube.

The cap will cover the tube with a calculated pressure to stay perfectly in place. It will also resist use-related stresses (chair legs, table or desk legs) more durably.

Taking measurements of a square, rectangular, or oval tube

Taking measurements of a hollow square or rectangular tube is done in two steps: the Outer dimensions and the Inner dimensions

In our range of square or rectangular inserts, choose the insert with the Outer dimensions that correspond exactly to the Outer dimensions measured on your tube. The insert will be flush with the tube (no protrusion or recession), which ensures an ideal aesthetic, perfect surface protection (for a foot insert) or person protection (for a finishing insert), as well as an optimal service life. This is the case for tube foot inserts, which must withstand significant weights and stresses. By being flush, the forces are correctly applied to the insert according to the usage conditions taken into account during their design.

Once you have found the insert with the Outer dimensions that correspond to those of your tube, ensure that the Inner dimensions of your tube are included in the range of Inner dimensions mentioned on the insert’s product page.

For example, for a square tube with measured Inner dimensions of 20x20mm, choose an insert with Inner dimensions of 19mm to 23mm. These dimensions are indicated on the insert technical sheets under the term ⧄Int (fin). It is essential that your tube’s Inner dimensions be within this range to guarantee a perfect fit.

In our range of external caps, choose the cap with the Outer dimensions that correspond exactly to the Outer dimensions measured on your tube. The cap will cover your tube with a calculated pressure to stay perfectly in position and resist use-related stresses over time.

Taking measurements of a solid square, rectangular, or oval tube requires measuring the Outer diameter

For a solid tube, whether square, oval, or rectangular, only external caps can be used. Choose the cap with the Outer dimensions (marked on the adjacent diagram as ⧄Ext) that correspond exactly to the Outer dimensions measured on your solid tube.

The cap will cover the tube with a calculated pressure to stay perfectly in place.

In conclusion

When replacing inserts or caps for chairs, tables, or for protecting profiles, taking good measurements is essential to choose the appropriate insert or cap. The Outer diameter or section is mandatory, and you should choose an insert or cap whose Outer dimensions are similar. For hollow tubes or profiles, the Inner diameter or section of the tube must be within the range of Inner dimensions mentioned in the description of the insert or cap.

If you are unsure or need advice on finding the right end cap, please contact our team via email (in the Contact section here) or by phone at +33 9 81 17 41 57 (Monday to Friday, 9 am to 6 pm). We will recommend the end cap or plug best suited to your specific situation.