Gauges are old measures of thickness. They originated in the British iron wire industry at a time when there was no universal unit of thickness. The sizes of the gauge numbers were the result of the process of wire-drawing and the nature of iron as a substance. Gauges were measured and described in fractions of an inch during the 19th century. In the UK, one gauge was standardised and legally enforced as the Standard Wire Gauge. One important reason for the standardisation of the gauge was the convenience of craftsmen. In the 20th century, the gauge was to be replaced with the introduction of the International System of Units. However, within the field of anaesthesia at the threshold of the 21st century, the gauge seems hard to remove from the minds of craftsmen like anaesthetists.