Table of plumbing connection size and steel pipe dimensions in mm
(∅ inside x ∅ outside)
|Outside diameter (mm)
|Wall thickness (mm)
|1″ or 4/4″
|1 1/4″ or 5/4″
|1 1/2″ or 6/4″
Table of insertion dimensions of the plumbing screw thread in a female fitting
|Length of BSPT tapered thread
|Inserting the thread (screw connection)
|15mm to 20mm
|9mm to 12mm
|16mm to 22mm
|9mm to 12mm
|19mm to 25mm
|10mm to 12mm
Calculate the size of a black or galvanised steel tube
In order to know the length of the tubes needed, add the reference value from the table above 10mm per thread for 1/2″ and 3/4″ tubes depending on the size of the plumbing fitting as these will be inserted into the female fitting and 11mm for 1″ tubes.
Example with an industrial suspension lamp
If a distance of 300mm is required between the centre tube and the centre of the E27 socket:
- You need to know the distance from the centre of the 90° elbow to the edge of the 90° elbow.
In this case we have opted for a plumbing fitting size of 1/2″ on the 90° elbow product sheet where you can find the dimensional diagram of the 90° elbow which informs us of a distance of 28mm.
For the equal tee fitting there is also 28mm.
- So subtract 2x 28mm (1x for the elbow and 1x for the tee) from our starting dimension (300mm) - this gives us 244mm.
This gives us the dimension between the 2 female elbow and tee fittings.
- Next we need to add the part that will be screwed into the female fittings on each side.
For this we take the value from the thread insertion table above.
In our case it is a 1/2″ plumbing fitting size so the reference value is 10mm which we add for each female fitting (1x elbow and 1x tee).
We will therefore need a 264mm pipe (10mm + 244mm + 10mm).
- If the dimensions of the final steel pipes are not to be precise as in this example we can opt for standard 250mm steel pipes and not 264mm custom made pipes.
This will save you extra manufacturing time and at the same time allow you to benefit from more attractive prices.