A brightly-coloured, adjustable woollen cloth belt worn in undress (barrack or working) uniform.
The use of such belts originated in the cavalry during the Victorian era when 'mucking out' stables was carried out in shirt sleeves. The cavalrymen's overalls were held up with braces, and the wear of such was uncomfortable whilst carrying out this hot and menial task. To counter this, troops started to manufacture their own work belts in their respective regimental colours and this gradually became accepted within the order of dress - migrating over to other regiments and corps in the latter part of the 19th century.
Stable belts can be found in varying widths and with differing methods of fastening: either side buckles or front plates. The latter seems to be on the wane due to Health and Safety reasons. They are found in a bewildering array of colours and patterns, from stripes to tartan. Most Commonwealth units have their own regimental or corps pattern.
They are generally a private purchase item, though it's understood that the RAF have recently made them an issue item. Money well spent!
Sometimes incorrectly referred to as a 'Staple Belt'.
All you need to know here: Stable Belts
REME stable belts have the unique distinction of doubling up as a bottle opener