It gives the best general holding power without needing anything done to the shaft first.

The sharp annular edge cuts into the shaft surface, so resistance to slip is mechanical rather than frictional.

It works on plain round shafts of ordinary hardness, which covers most drive, pulley and collar applications.

No spot drill, flat or machined feature is required, so it suits assemblies built without preparation.

It is also the most widely stocked point style in every thread size and material.

Where the shaft is hardened, thin-walled or must stay unmarked, one of the other point styles is the better answer.

It leaves a crater with a raised burr around it, and that burr is what stops the hub sliding off.

The mark is permanent. Removing it means dressing the shaft down with a file or stone before the component will pass.

On a shaft dismantled repeatedly, each reassembly bites in a slightly different place, so the marks accumulate along the seating length.

The damage is usually cosmetic in terms of shaft strength, but it matters wherever the shaft passes through a seal or a bearing.

Machining a flat at the set screw position confines the damage to one surface that can be dressed or accepted.

If the shaft genuinely must not be marked, a flat point with a shaft flat, or a clamping collar rather than a set screw, is the correct solution.

Not to make the screw work, but it improves almost everything about how the joint ages.

A flat gives a consistent seating position, so the hub returns to the same angular location each time it is assembled.

It confines the damage to one surface rather than spreading craters around the shaft.

It also increases contact area slightly, which reduces the tendency for the screw to walk under reversing loads.

A flat is easy to add on a lathe or with a file and is standard practice on shafts that see regular service.

On a hardened shaft a flat is often ground rather than machined, and the ground surface is still harder than the screw point.

It will not bite, so it holds by friction on a polished contact and much less reliably than published figures suggest.

The mechanism requires the screw to be harder than what it is biting into.

Against a hardened shaft the sharp edge flattens on first tightening and the screw becomes, in effect, a blunt flat point with a smaller contact area.

Set screws are supplied hardened precisely so they can bite ordinary shafting, and their hardness is stated.

On hardened shafts the usual answers are a dog point into a drilled hole, a flat point onto a ground flat, or a mechanical clamp.

Checking the hardness relationship before selecting a point style takes one look at two datasheets.

To the manufacturer's torque figure - and over-tightening deforms the point rather than improving the hold.

Contact is on a small annular ring, so even a modest torque produces very high local pressure, which is exactly how the point penetrates.

Past the point of full penetration, additional torque upsets the screw's own end and can strip the socket.

Socket damage is the usual failure on removal, because a rounded socket in a small headless screw is very difficult to extract.

Using the correct key, fully inserted, matters more here than on almost any other fastener.

Torque figures assume clean dry threads unless the manufacturer says otherwise.

Under vibration and reversing loads, yes - a single set screw is one of the less secure ways to hold a hub.

The joint is held by a small penetration and by thread friction, neither of which resists cyclic loading well.

Reversing torque is the worst case, because the hub works back and forth against the crater and enlarges it.

Two set screws at ninety degrees, or one plus a jam screw stacked above it in the same hole, are the traditional answers.

Thread-locking adhesive is effective and is standard practice on machinery assembly.

Where the load genuinely matters, a keyed shaft, a taper lock or a clamping hub carries torque far more reliably than any set screw.

Internal hex is the general standard; internal star takes more torque in the same size and is better on the smallest screws.

Because a set screw is headless, all the tightening torque goes through the socket, which is the weakest feature.

Internal hex sockets are universally available and adequate for most sizes.

Star drives engage more surface and resist rounding, which matters on very small screws where the socket is shallow.

Slotted set screws still exist and cam out easily; they suit low-torque adjustment rather than holding.

Whichever is chosen, the key must be fully seated - a partly inserted key rounds the socket on the first attempt.