These coupling nuts are manufactured in accordance to ASTM A563 standards.
The width across the flat is 13/16".
Yes you ran a bolt through the entire length.
The 1/4 in.-20 tpi Zinc Rod Coupling Nuts are sold under part number 822251. The following link shows the product and cost. https://www.homedepot.com/p/Everbilt-1-4-in-20-tpi-Zinc-Rod-Coupling-Nuts-822251/204337387
Coupling Nuts does not have a Tensile Strength. The Proof Load for this Coupling Nut is 100ksi.