[mactec54]

I found a couple of other useful resources; this (https://www.apexdyna.nl/en/the-right-timing-belt/) is a company based in Holland (so it'll have a Euro perspective) but seems to confirm that AT is good for my needs, and that GT is better known in the US market.

The Reprap wiki (https://reprap.org/wiki/Choosing_Belts_and_Pulleys) advises GT2 over T belts; which makes sense, and also perhaps confirms my guess that the better availability of the GT2 and GT3 parts in the UK is down to the popularity of 3D printers.

Given the relative lack of GT5 and GT10 here in the UK I'll proceed with AT. I've not found a suitable ATL belt yet (which I understand works with AT pulleys, and is even better than AT belts), but I am working my way through the various equations in the doc posted by Peter (which is proving very useful).

GT-2 and GT-3 series are the same, it was just a patent change GT-2 became GT-3, AT profile is the world over the GT series is also, if you know where to look, you don't need a ATL belt the belt won't change the backlash the AT Belts Pulleys have, and for what you are doing a regular AT Belt will work, the snip below tells you which Timing Belt is superior under tension and how much tension load each can take

You can see how wimpy the AT is in comparison

[sploo]

You can see how wimpy the AT is in comparison

That's T not AT though isn't it?

[mactec54]

That's T not AT though isn't it?

Yes T series is 40 Degree tooth the AT is 50 Degree tooth apart from that not much difference