On Thursday, May 2, 2019 at 4:29:14 PM UTC-4, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
On Monday, April 29, 2019 at 10:53:17 PM UTC-5, bumper wrote:
On Monday, April 29, 2019 at 6:31:00 AM UTC-7, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
I am not a qualified mechanical engineer to tell you it would carry the load but I would think that you could buy what you need at any steel supply house knowing the length and width/height plus, importantly, the wall thickness. Best of luck, John (OHM)

A piece of cake, really. If you don't happen to have metal working and welding equipment, any good shop should be able to put it together. A galvanizing place may be harder to find. If you prime and paint instead, suggest etching the steel with dilute phosphoric acid before painting. Jasco Metal Prep is available at many hardware stores or paint supply places. Paint it on, hose it off.

Thinking a little further on this, the square tube is bound to be a metric size. Getting an equivalent SAE sized tube may involve some effort. Slightly larger might not fit the internal brackets (or the AL-KO coupler). The better option is slightly smaller which will need some (welded on) thin shims to take up the slack - which the welding shop can handle (along with cutting off and reattaching the old jockey wheel bracket and underside's V shaped stand).

John OHM Ω

The current, square tube tow bar design (metric or imperial sized) can be improved by a lot. The hitch of a Cobra trainer is bolted on by two M12 bolts. The entire assembly is essentially coupled by friction. These bolts are not supposed to be in shear. Anyhow, one of the big draw-backs of square tubing is that the walls start to cave in when the bolts are being torqued.
Many moons ago, I did replace the rusted out tow bar of my trailer. I bought an equivalent stainless tube and drilled the holes for the hitch slightly larger than needed. Make sure not to drill through the tube's weld flash but 90* to it. Then I inserted short, tight fitting pieces of thick-walled SS-pipe trough the open end until they were aligned with the holes I drilled and TIG-welded them in place. Now I could torque the bolts holding the hitch to their appropriate value without deforming the square tubing.

Uli
'AS'