actually they
are in psi, of
stress area regarding tensile strength, so don't over-tighten .... but what counts for frame joints is
sheer strength - really more
important 
Bill
Not true, the tensile strength of the steel in the bolt is closer to 100ksi. Thats 100,000 pounds per square inch. If you look at the table it shows the area
that you will find by taking the minor or small diameter, at the root of the threads and use pi X r*2
that is pie times the radius squared. If it was a surface area of 1 inch then the load it would take is 100,000 pounds, that is if my 100ksi is true and correct. So then you take your area you just figured out 1/x it and divide that into the 100K to get the
actual stress that particular fastener bolt or rivet should take in tension.
I guess Bartamos figured out what the stress should be for the steel.
