Set screw

Example of set screws

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A set screw (British term is Grub Screw), is a type of screw generally used to secure an object within another object. It is generally fully threaded. A blind screw (or grub screw) will generally not have an external head and will be inserted into its location by means of an internal Hex, Allen, slot, Torx, star or Phillips key or driver. The set screw passes through a threaded hole in the outer object and is tightened against the inner object to prevent it from moving relative to the outer object. It exerts compressional or clamping force through the bottom tip that projects through the hole rather than with a larger head that remains outside.

A potentiometer knob with a set screw for locking it in place.

They are used to prevent relative motion between two rotating parts, such as the movement of pulley on a shaft. For this, a set screw is screwed into the pulley hub so that its end-point bears firmly against the shaft. The fastening action is by friction between the screw and the shaft.

Typically, set screws are not efficient and so are used only for transmitting very light loads. To reduce the chance of slipping and to increase load capacity, a detent may be drilled in the shaft into which the set screw's point enters. The detent, however, must be precisely aligned with the threaded hole prior to fastening. For longer life, they are usually made of steel and case hardened.

Isometric projection of a grub screw with a hex socket head.

Set screws appear with a variety of tip types. The different shaped tips have different properties that engineers can utilize. If an engineer were to use a detent to ensure proper nesting of the screw, they might choose to use a cone point type of screw. One might might often need to use a flat point when the screw must press perfectly flat against a surface. The most common type is the cup point. This type works well because the surface is rounded so that a small surface area is in contact, but it does not have extremely high stress at one point like that of a cone point. Durability studies show that the cup point offers superior resistance to wear while maintaining a strong grip.^[1]

Common points include the following:

• Flat Point
• Domed Point
• Cone Point
• Cup Point
• Knurled Cup Point
• Extended Point (Pilot Point, Dog Point)

They also appear with a variety of drive styles, including the following:

• Allen (hex)
• Square head
• Slotted
• Bristol spline

References

Notes

External links

Wikimedia Commons has media related to: Set screws

• Page illustrating various set screw tip types