The Screw Family – Almost Always Threaded, With an Exception

Screws are externally threaded, but there's one case where a screw might not be threaded at all.

Standard screws: Always threaded. Machine screws, wood screws, sheet metal screws, socket head cap screws – all have fully-formed helical threads. Many are self-threading: they create their own internal threads as they're driven in.

Thread-cutting vs. thread-forming screws: Both have threads. The difference is how they make their own mating hole. Thread-cutting screws physically remove material (you'll see chips). Some have pointed tips and don't require a pilot hole. Thread-forming or thread-rolling screws displace material rather than cutting it away. Both still have threads.

Threaded rods & studs: Fully threaded length of bar. No head. Threads on both ends. Definitely threaded.

The exception: Self-drilling screws and the "power-lag" with no threads? Actually no. Even self-drilling screws (Tek screws) have threads. The tip drills the hole, but the body above it still has threads to engage. The only fastener called a "screw" that truly has no thread is a set screw with a cup point used in some very light-duty applications – but that's not a thread; it's just a blunt tip with a hex socket. Even then, most set screws are threaded.

So for screws: yes, with the note that a very tiny subset of grub/set screws might have an unthreaded tip but still have threading along most of their length.

The Nut Family – Always Threaded (Internal)

Nuts are internally (female) threaded by definition. If it doesn't have an internal helical thread, it's not a nut.

A nut's entire job is to mate with the external thread of a bolt or stud. The internal thread profile is precisely matched to the bolt. Types include hex, lock, wing, acorn, flange, castle, and T-nuts. No thread = no nut.

The Washer Family – Not Threaded (but critical partners)

Washers are not threaded and never have been. They're flat or spring-like rings with a hole in the middle – smooth bore.

Types include flat washers, lock washers (split ring, toothed), fender washers, Belleville washers (conical spring washers). They distribute load, prevent loosening from vibration, and protect surfaces. If a washer had threads, it would be a threaded collar or a nut, not a washer.

The Rivet Family – Permanently Non-Threaded

Rivets are permanent non-threaded fasteners. Solid rivet, semi-tubular, split rivet, blind rivet ("pop rivet") – none have threads. They're installed by deforming the tail (bucking) or pulling a mandrel through a hollow body. The joint is permanent; you can't unthread a rivet.

Some "threaded rivets" exist (rivet nuts or threaded inserts), but they aren't pure rivets. They combine a blind installation method with an internal thread. Different category.

The Pin & Key Family – Never Threaded

Pins, keys, and retaining rings have no threads. They rely on friction, interference fit, or mechanical blocking.

Pin types: Dowel pins, taper pins, clevis pins, cotter pins, spring pins (rolled / slotted) – all non-threaded. Pins fit into pre-drilled holes, held by friction or tension.

Some pins (clevis pins) are held in place by a separate cotter pin or retaining ring – not by threads.

Keys: Woodruff keys, square keys, gib-head keys – rectangular blocks that fit into shaft keyways. No threads involved.

Retaining rings (snap rings / circlips): Internal or external – no threads. They sit in machined grooves and snap into place. E-rings and C-rings also non-threaded.

Specialty Fasteners – It Depends

This is where the "yes/no" answer gets loose. Many specialty fasteners are threaded; others aren't.

Threaded inserts: Helical coil inserts (Heli-Coil), key-locking inserts – internal threads. Definitely threaded.

Anchors: Expanding anchors in concrete – usually have an internal thread once installed, even if the body is a smooth shell. Toggle bolts are fully threaded.

Clips & clamps: Spring clips, hose clamps, panel clips – generally non-threaded, though some hose clamps have a threaded worm gear, which isn't a fastener thread in the traditional sense.

Nails & staples: No threads at all – purely friction.

Which Fasteners Have Threading – Quick Reference Table

Summary

Most mechanical fasteners that are designed for reuse and are not welded or permanently deformed have threads – bolts, screws, nuts, studs, and threaded inserts. But many common fasteners in construction, sheet metal assembly, and machine alignment are completely unthreaded: nails, staples, rivets, pins, keys, retaining rings, and most washers.

The rule of thumb:

Fastener type ends in "bolt" or "screw" → Almost certainly threaded.

Fastener name ends in "nut" → Internally threaded.

Fastener name contains "rivet", "pin", "key", or "ring" → Not threaded.

Washer → Never threaded (despite being used alongside threaded fasteners).

When in doubt, look for the helical ridge running around the shank. If you see it, it's threaded. If the surface is smooth – pin, rivet, nail, or plain ring.