On hardened shafts, thin walls, soft materials, and anywhere the joint is dismantled often.

It leaves no crater, so the shaft can be reassembled indefinitely without accumulating damage.

On a hardened shaft a biting point would flatten anyway, so nothing is lost by choosing flat deliberately.

On thin-walled tube a penetrating point dents or collapses the wall, which a flat face does not.

In brass, aluminium and plastics a cup point sinks in and destroys the seating surface.

It is also the right style when the screw is acting as a stop or a spacer rather than a clamp.

Substantially less than any biting point, because it holds by friction alone.

The difference is large rather than marginal, and it should be assumed rather than discovered.

On a plain round shaft the contact is close to a line at the tangent, which reduces the friction area further.

Against a machined flat with full-face contact, the holding power is far more respectable and often sufficient.

Higher torque helps but reaches the screw's own limits quickly.

Where friction alone is inadequate, a keyed shaft or a clamping hub is the correct answer, not a harder-tightened set screw.

In practice yes - without one, a flat point is often the weakest fixing in the assembly.

A flat gives full-face contact instead of tangential contact, which multiplies the friction area.

It also fixes the angular position, so the component returns to the same place on reassembly.

The flat should be at least as wide as the screw point and square to the tapped hole.

On hardened shafts the flat is ground rather than milled, and remains harder than the screw.

Where no flat is possible, a soft-tipped screw raises friction considerably without marking.

A set screw with a brass, nylon or other soft insert at the point, which grips well and protects the shaft.

The soft tip conforms to the shaft surface, so contact area is far larger than a hard flat face achieves.

It leaves no permanent mark, which is the whole point of choosing it.

Brass tips suit metal shafts and moderate temperature; polymer tips suit lighter duty and have their own temperature limits.

The insert wears and can be extruded under repeated tightening, so it is a consumable.

They are common in optical, instrument and finished-surface assemblies where a mark would be unacceptable.

Yes, and it is the correct style for it - the flat face bears squarely without digging in.

Set screws are frequently used to set an end position, limit travel or preload a bearing rather than to clamp a hub.

A biting point in that role would damage the surface it bears on and change the setting as it penetrated.

A flat face gives a stable, repeatable contact that can be adjusted and readjusted.

A locking method is usually needed, since an adjuster with no clamping load backs off readily.

A jam nut, a second screw or thread adhesive are the normal ways to hold the setting.

It needs help - friction on a flat resists rotation poorly, so a locking feature is usually necessary.

Thread-locking adhesive is the simplest and is standard practice in machinery assembly.

A jam screw stacked above the first in the same tapped hole is the traditional mechanical answer.

Nylon-patch set screws carry a prevailing-torque element on the thread itself and give a reusable lock.

Two screws at ninety degrees share the load and reduce the tendency to walk.

Where vibration is severe, the fixing method itself should be reconsidered rather than reinforced.

Not on its own - friction on a flat is not a way to transmit significant torque.

Set screws generally are a light-duty torque transmission method, and flat points are the lightest of them.

Under reversing or shock loads the hub works against the friction contact and eventually slips.

Once slip starts it polishes the contact and gets worse.

Keys, splines, taper locks and clamping hubs are the proper answers where torque is the point of the joint.

A set screw is often retained alongside those to prevent axial movement, which is a sensible use of it.