Ask the Expert – JIS Hex Flange Bolts & Hex Flange Nuts
Japanese manufacturers build their equipment with flange bolts and nuts that are made to the JIS (Japanese Industrial Standards) standards. The specifications that define the dimensions for JIS flange bolts and nuts are JIS B1189 (flange bolts) and JIS B1190 (flange nuts).
There was a major revision to both of these specs in 2005 that resulted in a change in the wrench size (width across the flats) that JIS flange bolts and nuts are made to.