Stainless Steel Allen Grub – Cup Point

Choosing the Right Allen Grub – Cup Point (Socket Set Screw)
1) What is an Allen grub – cup point & when to use it?

An Allen grub screw (socket set screw) – cup point is a headless screw with an internal hex drive and a hollow, concave tip (cup).

Use a cup point grub screw when you want to:

Lock one part onto another shaft (e.g., hub on shaft, collar on shaft)

Prevent rotation or sliding of components on a shaft/key

Have the screw sit fully below or flush with the surface (no projecting head)

Typical applications:

Couplings, collars, gears, pulleys on shafts

Lever arms, knobs, handles fixed to shafts

Machine tool fixtures and jigs

Locking adjustments on mechanical linkages

Cup point is the most common general-purpose point for set screws because:

The cup bites into the shaft slightly, giving good holding power

Contact is more localized than flat point, but less aggressive than cone or dog point

2) Environment & corrosion

Indoor / dry / machinery:

Use alloy steel (hardened) grub screws – cup point, usually black or lightly oiled.

Ideal for machine tools, automations, fixtures, couplings, collars in non-corrosive areas.

Outdoor / damp / mild chemical exposure / stainless shafts:

Use A2 (304) stainless grub screws – cup point.

Suitable for stainless shafts, outdoor mechanisms, light food plant applications.

Marine / chloride / aggressive wash-down:

Use A4 (316) stainless grub screws – cup point.

For marine shafts, coastal equipment, chemical/fume areas, food & pharma wash-down where corrosion is critical.

Simple rule:

High strength, dry indoor → alloy steel cup point

Corrosion resistance needed → A2 or A4 stainless cup point

3) Point style – why cup point (vs flat, cone, dog point)?

Cup point (your product):

End of the screw is concave, forming a cup.

Edge of the cup bites into the shaft surface, giving good resistance to rotation.

Best for general locking applications on shafts and collars.

Compared to:

Flat point:

End is flat → less damage to surface but lower holding power.

Used where frequent adjustment or minimal marking is required.

Cone point:

Sharp tip digs in deeply → maximum holding, but more shaft damage.

Used for permanent or high-vibration locking.

Dog point:

Cylindrical tip that fits into a hole or groove → positive drive location.

Used for indexing or precise location.

If a customer doesn’t specify, cup point is the default “locking on shaft” choice.

4) Length & thread engagement

Grub screws are specified as thread size × overall length (e.g. M6 × 10, M10 × 16).

When choosing length:

Ensure there is enough thread engagement in the tapped hole:

In steel: typically at least 1× screw diameter engagement as a practical rule.

In softer materials (aluminium, brass) → 1.5× diameter or more is safer.

Headless design means:

Once installed, the top of the grub screw can sit flush or slightly below the surface, so it doesn’t interfere with other parts.

Avoid:

Too short → limited engagement, risk of thread stripping.

Too long → screw may protrude out the other side or foul on rotating/adjacent parts.

Mechanical Properties (Guide) – Allen Grub Screw – Cup Point

Set screws (grub screws) are typically made from hardened steel or stainless, with properties optimised for surface hardness and strength rather than just property class like 8.8/10.9.

1) Alloy steel grub screws (hardened)

Typical characteristics:

Made from alloy or medium-carbon steel, heat-treated and tempered.

Often supplied to a hardness class similar to 45H (as per set screw standards), which corresponds roughly to mid-40s to low-50s HRC.

This gives:

High surface hardness → cup edge can bite into shaft.

Good tensile and shear strength along the threaded body.

Behaviour:

Excellent for locking and resisting rotation.

More resistant to tip wear and deformation under repeated tightening/loosening.

Should not be used where corrosion is severe unless surface-treated or in controlled conditions.

2) Stainless steel grub screws (A2 / A4)

Typical characteristics:

Material: A2 (304) or A4 (316) stainless.

Lower surface hardness than fully hardened alloy set screws, but:

Good corrosion resistance

Adequate strength for many locking applications

Typical strength:

A2-70 / A4-70 → tensile strength approx. 700 MPa range.

Proof strength lower than high-grade alloy, but usually sufficient for most collars, knobs, and medium-duty couplings.

Behaviour:

Ideal where rust and staining must be avoided (stainless shafts, food and pharma, marine).

May deform slightly more at the cup edge in very high-torque situations compared to hardened carbon steel.