It give the inch equivalents for the following systems:

  • Brown & Sharpe (which is American Wire Gauge, A.W.G.)
  • Washburn & Meon
  • Stub's Iron Wire (B.W.G.)
  • U.S. Standard Sheet
  • Stub's Steel Wire
  • Imperial Standard Wire Gauge (S.W.G.)
  • Birmingham Gauge for Sheets
  • American Steel & Wire Co. Music Wire
  • Engliush Music Wire

The reason wire (and sheet metal) gauges get smaller as the number increases is that the originated as the number of times a wire was pulled through a die to make it thinner (or sheets run through rollers). 18 gauge wire originally meant it had been pulled through 18 dies, so you can see how the use of different sets of dies led to different numberings (such as Birmingham Wire Gauge). SWG was introduced in the UK and AWG in North America to bring some standardisation, but sadly the opportunity to make both sides of the Atlantic the same was missed.

Click this link for a downloadable PDF from the Model Engineer Handbook, published by our predecessor company Percival Marshal in 1960.

Thanks to user Lambton for drawing this document to our attention and scanning it.