Full vs partial threaded machine screws

[jaz525]

I have some questions concerning machine screws. In what situations are full and partial threaded screws interchangeable? Does it matter which ones are used in a prestressed joint with no shear stress other than friction from threads etc? How about fatigue-wise with dynamic loads?

 

[TVP]

Partial threaded and fully threaded screws are not interchangeable for structural applications. If you have to perform calculations or testing in order to validate the joint, then they are not interchangeable. Fully threaded screws will have lower stiffness, and therefore change the load relation of the screw vs. the joint. Loosening and fatigue characteristics will vary depending on the manner in which the threads are rolled, meaning exact geometry of the threads, where the thread run out occurs along the shank, etc. Have you consulted any of the usual fastener references like Bickford & Nassar's Handbook of Bolts and Bolted Joints?

 

[chicopee]

Would not recommend partial threads on dynamic loads only full length threads.
Check out the Machinist Handbook for a formula on length of engagemnt for threads.