Set-Screw Information & Data

A set screw is a headless screw, typically driven with a hex key into a threaded hole in a collar, pulley, or hub, used to lock the component onto a shaft without needing a separate nut. Because it has no head to sit proud of the surface, a set screw is often the preferred choice where a projecting bolt head would be a clearance problem or safety hazard, such as on a rotating shaft. The tip of the screw is what actually grips the shaft, and different tip styles suit different jobs: a cup point bites in for a firm, semi-permanent grip; a flat point spreads load over a wider area for repeated adjustment without marking the shaft; and a dog point locates positively into a matching hole or slot machined into the shaft.

The chart below gives dimensional information on metric and imperial set screws, including head sizes and thickness.

Dimensional Charts for Metric Socket Set Screws, Metric Slotted Set Screws, Imperial Socket Set Screws, and Imperial Slotted Set Screws.

A set screw is a type of screw generally used to secure an object within or against another object. The most common examples are securing a pulley or gear to a shaft.

Set screws are usually headless (also called blind), meaning that the screw is fully threaded and has no head projecting past the major diameter of the screw thread.

A blind set screw or grub screw, is almost always driven with an internal-wrenching drive, such as a hex socket (Allen), star (Torx), square socket (Robertson), or slot.

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.

Dimensions shown are in Inches, if you wish to convert to mm, please use our universal converter.

SOCKET SET SCREW DIMENSIONS - METRIC - ASME/ANSI B18.3.6M

Nominal Size	Diameter (D)	Hex Size (S)	Key Engagement Cup (T1)	Key Engagement Oval (T2)	Across Corners (E)	Dog Point Length Max (P)	Dog Point Length Min (P)	Dog Point Dia (Dt)
M1.6	1.6	0.7	0.7	0.5	0.8	0.8	0.55	0.8
M2	2	0.9	0.8	0.6	1	1	0.75	1
M2.5	2.5	1.3	1.2	0.8	1.4	1.25	0.95	1.5
M3	3	1.5	1.2	0.8	1.7	1.5	1.15	2
M4	4	2	1.5	1	2.3	2	1.65	2.5
M5	5	2.5	2	1.2	2.9	2.5	2.15	3.5
M6	6	3	2.5	1.5	3.4	3	2.55	4
M8	8	4	3	2	4.6	4	3.5	5.5
M10	10	5	4	2.5	5.7	5	4.5	7
M12	12	6	4.8	3	6.9	6	5.5	8.5
M16	16	8	6.4	4	9.2	8	7.42	12
M20	20	10	8	5	11.4	10	9.42	15
M24	24	12	10	6	13.7	12	11.42	18

Nominal Size	Diameter (D)	Slot Width	Slot Depth	Dog Point Dia (Dt)
M1.6	1.6	0.25	0.56	0.8
M2	2	0.25	0.64	1
M2.5	2.5	0.4	0.72	1.5
M3	3	0.4	0.8	2
M4	4	0.6	1.12	2.5
M5	5	0.8	1.28	3.5
M6	6	1	1.6	4
M8	8	1.2	2	5.5
M10	10	1.6	2.4	7

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SOCKET SET SCREW DIMENSIONS - IMPERIAL - ASME/ANSI B18.3

Nominal Size	Diameter (D)	Hex Size (S)	Key Engagement Cup (T1)	Key Engagement Oval (T2)	Across Corners (E)	Dog Point Length Max (P)	Dog Point Length Min (P)	Dog Point Dia (Dt)
#0	0.06	0.028	0.05	0.04	0.032	0.03	0.025	0.028
#1	0.073	0.035	0.06	0.045	0.04	0.037	0.032	0.035
#2	0.086	0.035	0.06	0.045	0.04	0.043	0.038	0.043
#3	0.099	0.05	0.07	0.05	0.057	0.05	0.045	0.05
#4	0.112	0.05	0.07	0.05	0.057	0.056	0.051	0.057
#5	0.125	0.062	0.08	0.055	0.071	0.062	0.057	0.064
#6	0.138	0.062	0.08	0.055	0.071	0.069	0.064	0.07
#8	0.164	0.078	0.09	0.06	0.09	0.082	0.076	0.084
#10	0.19	0.094	0.1	0.065	0.108	0.095	0.088	0.097
1/4	0.25	0.125	0.125	0.075	0.144	0.125	0.115	0.127
5/16	0.3125	0.156	0.15	0.085	0.18	0.156	0.145	0.159
3/8	0.375	0.188	0.18	0.1	0.216	0.188	0.176	0.19
7/16	0.4375	0.219	0.21	0.115	0.252	0.219	0.205	0.222
1/2	0.5	0.25	0.25	0.13	0.289	0.25	0.235	0.254
5/8	0.625	0.312	0.32	0.17	0.361	0.312	0.295	0.318
3/4	0.75	0.375	0.42	0.22	0.433	0.375	0.355	0.381

Nominal Size	Diameter (D)	Slot Width	Slot Depth	Dog Point Dia (Dt)
#0	0.06	0.01	0.02	0.028
#1	0.073	0.012	0.024	0.035
#2	0.086	0.016	0.03	0.043
#3	0.099	0.019	0.035	0.05
#4	0.112	0.022	0.04	0.057
#5	0.125	0.026	0.045	0.064
#6	0.138	0.028	0.05	0.07
#8	0.164	0.032	0.06	0.084
#10	0.19	0.036	0.07	0.097
1/4	0.25	0.048	0.095	0.127
5/16	0.3125	0.06	0.115	0.159
3/8	0.375	0.072	0.135	0.19
7/16	0.4375	0.084	0.155	0.222
1/2	0.5	0.096	0.175	0.254
5/8	0.625	0.12	0.22	0.318
3/4	0.75	0.144	0.26	0.381

RELATED PAGES

• Fastener Tightening Torque Information
• Fastener Abbreviations
• Parallel Keys
• Engineering Glossary — Cup Point / Dog Point Set Screw

FREQUENTLY ASKED QUESTIONS

What's the difference between a set screw and a grub screw?

They're the same thing — "grub screw" is the more common term in the UK, while "set screw" is used more widely internationally, though in the US "set screw" specifically, and "cap screw" is sometimes used loosely for headed screws too, which can cause confusion between regions.

Which set screw tip should I use?

Cup point is the most common general-purpose choice, giving a good grip on a plain round shaft. Use a flat point where the screw will be adjusted repeatedly and you don't want to mark or damage the shaft. Use a dog point where the shaft has a matching drilled hole or flat, for the most positive location against rotation or axial movement.

How much torque should I apply to a set screw?

This depends on the screw size, material, and application — see our Fastener Tightening Torque Information page for general guidance, but always check the specific equipment manufacturer's recommendation where one exists.

Why does my set screw keep working loose?

Common causes include vibration, an incorrect tip style for the application, insufficient torque, or a shaft that's harder than the screw tip so it can't bite in properly. A thread locking compound, or switching to a dog point engaging a drilled flat, can help in persistent cases.