Few 1/4 -20 socket cap head screw with washers were tested for optimum torque.
QJR 117E Snap On torque wrench was used. I found that 40 lb in was enough.
These numbers will varie with washers, material it's going into and so on!
The standard among high-strength fasteners, these screws are stronger than Grade 8 steel screws. They have a minimum tensile strength of 170,000 psi. and a minimum Rockwell hardness of C37. Length is measured from under the head.
Inch screws have a Class 3A thread fit. They meet ASTM A574.
Black Oxide—Screws have been heat-treated for hardness, which results in a dark surface color.
Rana is next to calibrate his feelings and declare the right number.
Than Koji....and so on
Once we a number, than I buy more torque wrenches to fit it.