For the BCA we can supply a 7mm diameter length of solid round plastic belt made in Switzerland. This has a high-grip, rough green finish and is designed especially for machine -tool drives. The BCA Mk.3 normally takes a 1.7m length - but if you have a MK.1 or a Mk.2 it would be better to measure the length you need carefully. We can supply the belt joined for an extra £3.00 + VAT - which, at this diameter, we would recommend as the spindle is easily dismantled. See:  http://www.lathes.co.uk/bca for illustrations of the assembly
You can buy the 1.7 m belt ready joined on this page -  but if you need a different one order here. https://store.lathes.co.uk/belts/solid-round-plastic-belts