A plastic caster with BZP steel stem. Fix to your 1 1/4" pipe using a Caster Cap
£4.27 (£5.12 inc VAT)
The caster and cap are simple to attach: the caster has a shaft which is pushed through a hole in the caster cap, where it then locks in place. The caster can then spin around and act as a wheel without risk of falling out. Pipe is able to slot into the other side of the caster cap so that your structure can be built up from there.
These fittings are also available to special order in different colours, which allows for colour coded organisation of trolleys in a medical facility, for example. Different areas of a facility can have different coloured trolleys - so when a red trolley is found in a yellow area, it is easily spotted and moved back to the red area, avoiding cross-contamination.
The caster and cap fittings are only available in the 1 1/4" size. It is also important to note that the pipe size which goes into the cap is a North American specification; therefore, a standard pipe you might buy in a local DIY store won't be compatible with these fittings, because they won't have been manufactured in North America to their specifications.
For a permanent application, these fittings can be glued together, or they can be fixed temporarily together using plastic rivets.