Pentalobular screw thread

Self-tapping screws are widely used for driving into sheet metal or plastics and forming their own thread.

Others work not by cutting, but rather by roll-forming the thread, pushing excess material out of the way by plastic deformation.

[2] The proportions of the lobular thread can also change over the length of the screw, so that the tip of the screw can use greater lobulation to form the thread more aggressively and also provide a centring effect.

[1] Their number should be prime, to avoid the usual harmonic effects between lobes.

As is already widely recognised with tapered reamers, five has better stability than three in imperfectly circular holes.

Axial view of a ■ pentalobular thread between the ■ minimum and ■ maximum diameters for the formed thread. The difference in minimum and maximum radii has been exaggerated (doubled) for illustration.