Why Some Screws Have a Partially Threaded Shank

Consisting of a head, shank and tip, screws are one of the world’s most commonly used fasteners. Like bolts, they are designed to connect multiple objects or surfaces together. When comparing the different types of screws, though, you may notice that some of them all have a partially threaded shank.

What Is the Shank?

The shank is the long and narrow body of a screw that connects the head to the tip. Most screws have a fully threaded shank that’s defined by helical ridges. The physical distance between each of these interconnected helical ridges is known as the pitch With a fully threaded shank, the screw can be driven all the way into the object or surface with which it’s used.

Some screws, however, only have a partially threaded shank. A common example is a wood screw. Defined for use with wooden objects and surfaces, wood screws typically have about three-quarters of their shank threaded, with the remaining one-quarter of their shank being smooth and unthreaded.

Reasons for a Partially Threaded Shank

The partially threaded shank isn’t a design flaw. Rather, it allows for a stronger hold than that of fully threaded screws. Partially threaded screws still work in the same way as their fully threaded counterparts. You press the tip against the object or surface, at which point you can use a tool — such as a screwdriver — to turn and drive the screw into the respective object or surface. With a partially threaded shank, however, the screw will come to a stop after the end of the threading. With a fully threaded shank, on the other hand, there’s nothing to stop the screw. The bottom line is that partially threaded screws offer a stronger hold than fully threaded screws.

Partially threaded screws can also be used with nuts and washers for additional strength and stability. They feature the same basic design as fully threaded screws, with the only difference being that part of their shank is threaded. As a result, standard nuts and washers will fit around a partially threaded screw.

In Conclusion

Some screws have a partially threaded shank to protect them against loosening. When driven into an object or surface, they’ll stop automatically after reaching the end of the threading. And like fully threaded screws, they can be used either with or without nuts and washers.

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