All I've been able to determine is it is specified under DIN 13. http://www.sparkfix.com.br/ganter/kate/13.htm
Unless someone has a copy of the standard and they can look up in it its meaning and origins, you may have to buy it to find out. Or maybe a local library has a copy of it. Euric ----- Original Message ----- From: "John S. Ward" <[EMAIL PROTECTED]> To: "U.S. Metric Association" <[EMAIL PROTECTED]> Sent: Thursday, 2004-01-29 22:58 Subject: [USMA:28448] Metric hole and shaft tolerances > Does anyone have a good explanation of metric hole and shaft tolerancing (like > H7/g6, etc.)? There are tables floating around on the internet that allow > one to determine actual size ranges from the call-outs, but I still find this > system to be cryptic and unnaturally complicated. Who invented this system? > What's the rational for the various letter and number combinations? How > common is this system world-wide? Why does it look so similar to thread > tolerancing? Surely there's a better way! > > John > > On Wednesday 28 January 2004 15:29, Chimpsarecute wrote: > > Default metric fastener thread tolerance class. If thread tolerance class > > designation (e.g., "-6g") is omitted (e.g., M10 x 1.5), it specifies > > "medium" thread tolerance, which is 6H/6g. The 6H/6g fit is the standard > > ISO tolerance class for general use. > >
