Heavy hex jam nuts have the same dimension across the flats as heavy hex nut, but are thinner.
Hardware ASTM A325
Die Seams on Headed Bolts - Portland Bolt
Grooving Tools - Portland Bolt
Fastener Marking Requirements - Portland Bolt
Nuts, Bolts, and Screws
7/8-9 Coarse Thread A194 Grade 2H Heavy Hex Nut - USA Medium
Nuts Selection Guide: Types, Features, Applications
Recommended Nuts and Washers - F1554 Anchor Bolts
Step Bolts - Portland Bolt
Coupling Nut Grades - Portland Bolt