A six-sided internally threaded, fastener with a metric thread pitch. The jam nut is approximately 1/2 the thickness of a Style 2 nut. Nuts are chamfered on the top and on the bearing surface. Class 50 stainless metric hex jam nuts are tightened against the work surface and a Style 1 or Style 2 hex nut is tightened against the jam nut to keep it from loosening.