ORIGINAL: Dr1Driver
Diameter isn't what handles load, area is - and there's a big difference there.
Almost twice.
That is correct for tension and compression strength, which are proportional to the sectional area.
For avoiding buckling, the diameter is more important than the area, since rigidity depends on the section's inertia module, or how far from the center the material is.
That is why a tube is more resistant to buckling than a rod of similar sectional area.
Since that section's inertia module is proportional to radius^4, for similar ideal conditions, the 2-56 threaded rod will fail due to buckling at only 30% of the compression force that would make a 4-40 threaded rod fail by buckling.
Thanks for the correction, Dr1Driver; the small difference in diameter does make a big difference for practical use.
I have corrected my previous post.
ameyam,
Good reading here:
http://www.airfieldmodels.com/inform...ware/index.htm