Screw thread
A screw thread, often shortened to thread, is a helical structure. It is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread.
The tightening of a nut to a bolt is like driving a wedge into a gap until it sticks through friction and plastic deformation (how the surfaces of the two objects slightly squash together).
A screw thread is one of the six simple machines which give mechanical advantage.
The mechanical advantage of a screw thread depends on its lead, which is the linear distance the screw travels in one turn or revolution.[1]
Screw Thread Media
Screw thread, used to convert torque into the linear force in the flood gate. The operator rotates the small vertical bevel gear in the center. Through mechanical advantage this causes the horizontal bevel gears (at far left and far right, with threaded center holes) to rotate. Their rotation raises or lowers the two long vertical threaded shafts - as they are not free to rotate.
Right- and left-handed screw threads
The right-hand rule of screw threads
Different (and incompatible) threads including (from left) M12 left hand, standard M12, M12x1.5 (fine), M12x1.25 (fine), 1/2" UNF, 1/2" UNC, 1/2" BSW, and 1/2" BSF
Lead and pitch for two screw threads; one with one start and one with two starts
Up to four starts are labeled with different colors in this example.
Camshaft cover stud threaded 1⁄4-20 UNC (left, for aluminium cylinder head) and 1⁄4-28 UNF (right, for steel nut; from a 1960s Jaguar XK engine)
The three diameters that characterize threads
Sign ⌀ in a technical drawing
The basic profile of all UTS threads is the same as that of all ISO metric screw threads. Only the commonly used values for Dmaj and P differ between the two standards.
References
- ↑ Burnham, Reuben Wesley (1915). Mathematics for Machinists. John Wiley & sons, Incorporated. p. 137.