Nuts and Bolts . Threaded Fastener Issues: Types Materials/Grades Tightening Torque. Threaded Fasteners. Did you know that? the Boeing 747 uses about 2.5 million fasteners 70,000 titanium costing $150,000 400,000 other fasteners costing about $250,000
Threaded Fastener Issues:
Did you know that?
Unified or American ACME
Pipe Whitworth (UK)
1/2â€ť - 13 UNC - 2A
Terminology of screw threads
Sharp vee threads shown for
clarity; the crests and roots are
actually flattened or rounded
during the forming operation.
(B means internal)
Class of fit
(1 is loosest tolerance, 3 is tightest)
UNC (Unified Coarse)
UNF (Unified Fine)
(also shown as decimal or screw #)
It is typical on engines for bolts to have a specified tightening torque. Why?
Thread-rolling processes: a) reciprocating flat dies; and b) two-roller dies.
Threaded fasteners, such as bolts, are made economically by these
processes at high rates of production
(a) Differences in the diameters of machined and rolled threads. (b) Grain flow in machined and rolled threads. Unlike machining, which cuts through the grains of the metal, rolled threads have improved strength because of cold working and favorable grain flow.