Everything You Never Wanted To Know About Pipes and Tubes

It goes by many names, but 1.9” or 48.26mm steel tube is one of the most cost-effective materials available for building exercise equipment or, frankly, anything structural.  All of the following specifications point to the same thing, steel tube with a 48.26mm outer diameter:

  • 1 ½” Nominal Bore Pipe 
  • DN40 Pipe 
  • Scaffolding Tube 
  • Size 4 Handrail 
  • Strongman Axle (No coincidence)

A little bit of history:  Pipes are often sized on the internal diameter, because that is what flow calculations are based on, and pipes are generally used for conveying fluids.  Pipe with this outside diameter (1.9”) originally had an internal diameter of 1½”, which is how it became known as 1½” pipe.  This pipe had a hefty wall thickness because steel was weaker and less consistent in quality than it is now.  As material quality improved, the walls could be made thinner depending on the application.  Because the ends of the pipe were usually threaded or had flanges welded to them, it made sense to keep the outside diameter the same to preserve uniformity of threads and fittings.  Therefore, the inside diameter was manipulated to change the wall thickness.  As a result, one-and-a-half-inchyness was no longer a standard feature of one-and-a-half-inch pipe.  

Now, when you have a standard where the name is based on a measurement that is often completely absent from the thing being standardized, the next step is to apply the metric system to further complicate things.  So our European friends and neighbors have the equivalent DN40 pipe.  DN stands for ‘Diametre Nominal’ (say it with your best Pepe Le Pew accent).  The 40 refers to 40mm, which is close enough to 1.5” when measurements are imaginary.

The wall thickness (and therefore the internal diameter) is dictated by the “Schedule” of the pipe.  The most commonly available are Schedule 40 aka “Standard“ which (for 1½” pipe)  has a wall thickness of 0.145”/3.7mm and Schedule 80 aka “Extra Strong”, which has a wall thickness of 0.2”/5.1mm (this actually DOES have a 1.5” inner diameter).  Other Schedules from 5 to 160 exist, but are less common.

Pipe is commonly available as stainless steel, plain steel, galvanized steel, steel with red oxide primer and steel with shitty flaky black paint.

This size has been appropriated for use in old fashioned tube-and-coupler scaffolding systems as well as the largest size of handrail (size 4).  This is generally either galvanized steel or aluminium alloy, with wall thicknesses in the 3.2-4mm range.  In the UK this is available in various lengths from 4’ up to 6m (if you are uncomfortable with mixing imperial and metric units, don’t live in the UK, where plywood comes in 8’x4’ sheets and plasterboard/sheetrock comes in 1.2mx2.4m sheets, so whatever stud spacing you pick, it is wrong.)  Galvanized steel scaffolding tubes can be found in the UK for as little as 75 pence per foot, which is often cheaper than 2×4 and is always straight.  It can live outside indefinitely and is extremely versatile. 

The benefit of all this is that 1.9” OD pipe is available from a wide range of suppliers, which also stock a wide variety of fittings that can be threaded, welded or clamped to the pipe.

Scaffolding Fittings:  This is the most cost effective and versatile method for connecting lengths of tube.  These are very cheap in the UK, with 90 degree couplers costing around a pound, and swivel couplings slightly more.  The fittings have a high load rating and can be reused repeatedly.  They are meant to live outside in all conditions.  Pipes don’t need to be cut to exact lengths, as they just protrude a bit.  The downside is that when two pipes are joined at an angle, they are offset from each other, which has to be planned for.  Always check the specification of the fittings and apply the proper standards.  Fittings are also available for securing scaffolding to girders, plywood, walls, and scaffolding boards (good value in their own right and can be delivered alongside tubes and fittings).  These can potentially be reappropriated for many home gym uses. I use single “wrapover” couplings as J-hooks (slightly modified) and as spotter supports (along with smaller “Size 3” handrail, which is small enough to slide through).

J Hook From Modified Fitting
Spotter with Size 3 Handrail

Handrail Fittings:  While aesthetically more pleasing than scaffolding fittings, they are more expensive, require pipes to be cut to length and don’t have the holding strength, generally being secured by hex-key grub screws.  The feet are pretty useful for the base of equipment and they can be used to adapt from the scaffolding tube down to smaller diameter tubes, which is handy for pull up bars etc.

Welded Fittings:  Welded fittings are available as bends, reducers, tees etc. as well as slip-on and butt-weld flanges (which have their own fun sets of standards).   

Pull Up Bar Made From Handrail Fittings

Threaded Fittings:  The ends of the pipe can be threaded with either a tapered or parallel thread.  The most common threads are:

  • 1 ½” British Standard Pipe- Parallel (BSPP)
  • 1 ½” British Standard Pipe – Tapered (BSPT)
  • 1 ½”  American National Standard Taper Pipe Thread (NPT, because ‘National’ always implies ‘American’ unless otherwise stated). 
  • 1 ½”  American National Standard Straight Pipe Thread (NPS)

A wide variety of threaded flanges, couplings, adaptors etc are available.  Of most interest to people looking to build strength training equipment would be flanges which can be used to screw pipe sections to walls or timber or as fixed inner collars for axle bars. Here I have used a flange to make a loading pin

Loading Pin