← ArticlesMachine Screws, Cap Screws and Set Screws: Mechanical Properties Standards ReferenceEngineering · Machine DesignLesson 24/53← PrevNext →
GuidePublished 14 Aug 202622 min readBy Kevin JoginMachine DesignFasteners and JointsMachine ScrewsCap Screws and Set Screws

Engineering · Machine Design · Fasteners and Joints

Machine Screws, Cap Screws and Set Screws: Mechanical Properties Standards Reference

Engineering handbook for machine screws, cap screws and set screws, covering mechanical properties standards reference, ansi/asme standards covered, british...

25 min read Handbook guide Reviewed 2026-08-14

Executive summary

This handbook section converts the supplied engineering material into a practical, source-controlled reference. It concentrates on the following learning outcomes.

Mechanical Properties Standards Reference
ANSI/ASME Standards Covered
British Standards Covered
Your Next Step
What Exactly Is a Machine Screw?
The ANSI Head Type Encyclopedia

Mechanical Properties Standards Reference

ANSI/ASME Standards Covered

Standard Covers
ANSI/ASME B18.6.2-1998 Slotted head cap screws and slotted headless set screws
ANSI/ASME B18.3-1998 Hexagon and spline socket head cap screws, flat countersunk head cap screws, button head cap screws, shoulder screws, and socket set screws

British Standards Covered

Standard Covers
BS 4168:Part 1:1981 Hexagon socket head cap screws — metric series
BS 4168:Part 2:1994 Hexagon socket set screws, flat point
BS 4168:Part 3:1994 Hexagon socket set screws, cone point
BS 4168:Part 4:1994 Hexagon socket set screws, dog point
BS 4168:Part 5:1994 Hexagon socket set screws, cup point
BS 4168:1967 Countersunk and button head cap screws — metric
BS 6104:Part 1:1981 Mechanical properties — bolts, screws, studs (carbon/alloy steel)
BS 6104:Part 2 Mechanical properties — set screws and similar (not under tensile stress)
BS 6104:Part 3 Mechanical properties — class 45H for set screws
BS 6105:1981 Corrosion-resistant steel fasteners (austenitic, ferritic, martensitic)

Your Next Step

Print the holding power formula card. Laminate it. Tape it inside your toolbox.

P=D×N×d2.350T=1250×D×d2.3\boxed{P = \frac{D \times N \times d^{2.3}}{50}} \quad \boxed{T = 1250 \times D \times d^{2.3}}

The next time you reach for a set screw, run the numbers. Five seconds of calculation prevents five hours of downtime — or five months of explaining what went wrong.

What is the most critical set screw application in your shop right now? Have you verified that the screw can carry the load?

If the answer is no, you now have everything you need to check. The standards are in front of you. The formulas are in your hands. The decision matrix is ready.

Make the practitioner's lesson yours — without needing the grinding noise and the smoke.

What Exactly Is a Machine Screw?

Before you can master machine screws, you need to understand what separates them from every other threaded fastener in the catalog.

A machine screw is a threaded fastener designed to be driven into a tapped hole or secured with a machine screw nut. Unlike wood screws (which form their own threads in soft material) or self-tapping screws (which cut or form threads as they're driven), machine screws are intended for pre-threaded mating surfaces.

The governing standard is ANSI B18.6.3-1972 (R1991), which covers both slotted and recessed head machine screws. This standard defines dimensions for all major head types, machine screw nuts, header points, cross recess dimensions, and gaging dimensions.

Here's what defines a machine screw:

  • Thread type: Unified Coarse (UNC) or Fine (UNF), Class 2A — or UNRC and UNRF Series, at the manufacturer's option
  • Size range: #0000 (0.0210 in.) through 3/4 in. (0.7500 in.) in inch series; M2 through M12 in metric series
  • Body diameter: Not less than Class 2A minimum pitch diameter, and not greater than the basic major diameter of the thread
  • Head types: Flat countersunk, oval countersunk, pan, fillister, truss, binding, hex, hex washer, and round (obsolescent)

Key distinction: Sizes #0000, #000, and #00 use special NS (National Special) threads with dimensions defined separately in the standard appendix.

The ANSI Head Type Encyclopedia

This is where the practitioner's mistake happened. And it's where most machine screw errors originate.

Every head type exists for a specific engineering purpose. Choose the wrong one and you've introduced a clearance problem, a torque limitation, a cosmetic defect, or a structural weakness into your design.

Flat Countersunk Head (82°)

The flush-mount workhorse.

The flat countersunk head sits flush with—or slightly below—the mating surface when driven into a properly countersunk hole. The conical bearing surface has an included angle of approximately 82 degrees.

When to use it: Any application requiring a smooth, flush surface. Enclosures, panels, cover plates, and any cosmetic assembly where a protruding head is unacceptable.

Critical design consideration: The nominal length of a flat countersunk head screw is measured from the top of the head to the end of the shank—not from the underside of the head. This is different from pan head and fillister head screws where length is measured from the underside.

Nom. Size Basic Dia. Head Dia. (Max) Head Dia. (Min) Head Height (Ref.) Slot Width (Max) Slot Depth (Max)
#0 0.0600 0.119 0.099 0.035 0.023 0.015
#2 0.0860 0.172 0.147 0.051 0.031 0.023
#4 0.1120 0.225 0.195 0.067 0.039 0.030
#6 0.1380 0.279 0.244 0.083 0.048 0.038
#8 0.1640 0.332 0.292 0.100 0.054 0.045
#10 0.1900 0.385 0.340 0.116 0.060 0.053
1/4 0.2500 0.507 0.452 0.153 0.075 0.070
5/16 0.3125 0.635 0.568 0.191 0.084 0.088
3/8 0.3750 0.762 0.685 0.230 0.094 0.106
1/2 0.5000 0.875 0.775 0.223 0.106 0.103
5/8 0.6250 1.125 1.002 0.298 0.133 0.137
3/4 0.7500 1.375 1.230 0.372 0.149 0.171

All dimensions in inches per ANSI B18.6.3-1972 (R1991).

Undercut heads: For short screw lengths, the head height is reduced (undercut) to provide greater thread engagement. The maximum lengths at which undercut heads apply are specified per size—for example, #0 screws 1/8 in. and shorter receive undercut heads.

Degree Flat Countersunk Head

The aircraft-industry alternative.

Where the standard 82-degree countersunk head doesn't provide sufficient bearing area or head strength, the 100-degree flat countersunk head offers a shallower cone angle with a wider spread. The included angle of 99° to 101° creates a lower-profile countersink pocket.

Nom. Size Basic Dia. Head Dia. (Max) Head Dia. (Min) Head Height (Ref.) Slot Width (Max) Slot Depth (Max)
#0 0.0600 0.119 0.096 0.026 0.023 0.013
#4 0.1120 0.225 0.191 0.049 0.039 0.024
#6 0.1380 0.279 0.238 0.060 0.048 0.030
#8 0.1640 0.332 0.285 0.072 0.054 0.036
#10 0.1900 0.385 0.333 0.083 0.060 0.042
1/4 0.2500 0.507 0.442 0.110 0.075 0.055
3/8 0.3750 0.762 0.670 0.165 0.094 0.083

All dimensions in inches per ANSI B18.6.3-1972 (R1977).

Close tolerance variant: A close tolerance 100-degree flat countersunk head is also standardized for precision applications, providing tighter dimensional control on head diameter.

Pan Head

The modern standard. Use this for new designs.

The pan head features a flat top surface that rounds into cylindrical sides, with a flat bearing surface underneath. It has replaced the round head as the preferred general-purpose protruding head style.

Why pan heads replaced round heads: Superior slot driving characteristics. When you apply torque to a slotted pan head, the driver engages more positively than with a round head. The flat top provides better visual alignment indication, and the cylindrical sides create a more defined bearing surface.

Nom. Size Basic Dia. Head Dia. (Max) Head Dia. (Min) Head Height (Max) Head Height (Min) Head Radius (Max) Slot Width (Max) Slot Depth (Max)
#0000 0.0210 0.042 0.036 0.016 0.010 0.007 0.008 0.008
#000 0.0340 0.066 0.060 0.023 0.017 0.010 0.012 0.012
#00 0.0470 0.090 0.082 0.032 0.025 0.015 0.017 0.016
#0 0.0600 0.116 0.104 0.039 0.031 0.020 0.023 0.022
#1 0.0730 0.142 0.130 0.046 0.038 0.025 0.026 0.027
#2 0.0860 0.167 0.155 0.053 0.045 0.035 0.031 0.031
#4 0.1120 0.219 0.205 0.068 0.058 0.042 0.039 0.040
#6 0.1380 0.270 0.256 0.082 0.072 0.046 0.048 0.050
#8 0.1640 0.322 0.306 0.096 0.085 0.052 0.054 0.058
#10 0.1900 0.373 0.357 0.110 0.099 0.061 0.060 0.068
1/4 0.2500 0.492 0.473 0.144 0.130 0.087 0.075 0.087
5/16 0.3125 0.615 0.594 0.178 0.162 0.099 0.084 0.106
3/8 0.3750 0.740 0.716 0.212 0.195 0.143 0.094 0.124
1/2 0.5000 0.987 0.958 0.281 0.260 0.175 0.106 0.161
3/4 0.7500 1.435 1.375 0.419 0.390 0.263 0.149 0.234

All dimensions in inches per ANSI B18.6.3-1972 (R1991).

Fillister Head

Maximum slot depth in minimum head diameter.

The fillister head has a rounded top surface, cylindrical sides, and a flat bearing surface. Its distinguishing feature is the relatively tall head height compared to its diameter, which provides an exceptionally deep slot. This deeper slot engagement resists cam-out during high-torque driving.

When to use it: Applications requiring high driving torque where slot cam-out is a concern. Also used where a small-diameter protruding head is acceptable and a deep slot is needed for driver engagement.

Drilled fillister variant: A drilled fillister head includes a cross-drilled hole through the head for lockwiring. This is critical in aerospace and military applications where vibration could loosen the screw.

Nom. Size Basic Dia. Head Dia. (Max) Head Dia. (Min) Head Side Ht. (Max) Head Side Ht. (Min) Total Head Ht. (Max) Total Head Ht. (Min) Slot Width (Max) Slot Depth (Max)
#0 0.0600 0.096 0.083 0.043 0.038 0.055 0.047 0.023 0.025
#2 0.0860 0.140 0.124 0.062 0.053 0.083 0.066 0.031 0.037
#4 0.1120 0.183 0.166 0.079 0.069 0.107 0.088 0.039 0.048
#6 0.1380 0.226 0.208 0.096 0.086 0.132 0.111 0.048 0.060
#8 0.1640 0.270 0.250 0.113 0.102 0.156 0.133 0.054 0.071
#10 0.1900 0.313 0.292 0.130 0.118 0.180 0.156 0.060 0.083
1/4 0.2500 0.414 0.389 0.170 0.155 0.237 0.207 0.075 0.109
3/8 0.3750 0.622 0.590 0.253 0.233 0.355 0.315 0.094 0.164
1/2 0.5000 0.750 0.710 0.297 0.273 0.412 0.362 0.106 0.190
3/4 0.7500 1.000 0.945 0.441 0.406 0.612 0.542 0.149 0.281

All dimensions in inches per ANSI B18.6.3-1972 (R1991).

Oval Countersunk Head

Flush profile with a decorative crown.

The oval countersunk head combines the conical bearing surface of a flat countersunk head with a raised, rounded top surface. The screw sits in a countersunk hole, but the dome protrudes above the surface for a finished, decorative appearance.

When to use it: Decorative panels, finished hardware, visible enclosures where a completely flush surface isn't required but a polished appearance is essential. The raised dome prevents scratching from objects sliding across the surface.

Nom. Size Basic Dia. Head Dia. (Max Edge Sharp) Head Dia. (Min Edge Rounded) Head Side Height (Max) Total Head Height (Max) Slot Width (Max) Slot Depth (Max)
#0 0.0600 0.119 0.099 0.025 0.046 0.023 0.028
#2 0.0860 0.172 0.147 0.036 0.065 0.031 0.040
#4 0.1120 0.225 0.195 0.047 0.084 0.039 0.053
#6 0.1380 0.279 0.244 0.059 0.104 0.048 0.065
#8 0.1640 0.332 0.292 0.070 0.123 0.054 0.078
#10 0.1900 0.385 0.340 0.081 0.142 0.060 0.090
1/4 0.2500 0.507 0.452 0.107 0.186 0.075 0.119
3/8 0.3750 0.762 0.685 0.161 0.278 0.094 0.179
1/2 0.5000 0.875 0.775 0.156 0.288 0.106 0.204

All dimensions in inches per ANSI B18.6.3-1972 (R1991).

Truss Head

Maximum bearing surface for thin materials.

The truss head features a low, wide profile with a rounded top surface. The head diameter for a given screw size is significantly larger than the corresponding round head—providing maximum bearing area to distribute load across thin or soft materials.

Industry note: The truss head is considered an inherently weak design due to its low profile. It is not recommended for new designs per the ANSI standard. However, it remains in wide use for sheet metal applications where bearing area matters more than head strength.

Nom. Size Basic Dia. Head Dia. (Max) Head Dia. (Min) Head Height (Max) Head Height (Min) Head Radius (Max) Slot Width (Max) Slot Depth (Max)
#0 0.0600 0.131 0.119 0.037 0.029 0.087 0.023 0.022
#2 0.0860 0.194 0.180 0.053 0.044 0.129 0.031 0.031
#4 0.1120 0.257 0.241 0.069 0.059 0.169 0.039 0.040
#6 0.1380 0.321 0.303 0.086 0.074 0.211 0.048 0.050
#8 0.1640 0.384 0.364 0.102 0.088 0.254 0.054 0.058
#10 0.1900 0.448 0.425 0.118 0.103 0.283 0.060 0.068
1/4 0.2500 0.573 0.546 0.150 0.133 0.375 0.075 0.087
3/8 0.3750 0.823 0.787 0.215 0.191 0.538 0.094 0.124
1/2 0.5000 1.073 1.028 0.280 0.250 0.701 0.106 0.161
3/4 0.7500 1.573 1.511 0.410 0.368 1.024 0.149 0.234

All dimensions in inches per ANSI B18.6.3-1972 (R1991).

Binding Head

The wire-management specialist.

The binding head features a slightly undercut shoulder beneath the head with a very low oval top. Designed specifically to clamp and organize wires, cables, and harnesses against a surface. The undercut provides a channel for the wire to sit in, while the low-profile head minimizes protrusion.

Nom. Size Basic Dia. Head Dia. (Max) Head Dia. (Min) Total Head Ht. (Max) Total Head Ht. (Min) Oval Ht. (Max) Oval Ht. (Min) Slot Width (Max) Slot Depth (Max)
#0 0.0600 0.126 0.119 0.032 0.026 0.012 0.008 0.023 0.018
#2 0.0860 0.181 0.171 0.050 0.043 0.018 0.013 0.031 0.030
#4 0.1120 0.235 0.223 0.068 0.061 0.025 0.018 0.039 0.042
#6 0.1380 0.290 0.275 0.087 0.078 0.032 0.024 0.048 0.053
#8 0.1640 0.344 0.326 0.105 0.095 0.039 0.029 0.054 0.065
#10 0.1900 0.399 0.378 0.123 0.112 0.045 0.034 0.060 0.077
1/4 0.2500 0.525 0.498 0.165 0.152 0.061 0.046 0.075 0.105
3/8 0.3750 0.788 0.746 0.253 0.235 0.094 0.071 0.094 0.163

All dimensions in inches per ANSI B18.6.3-1972 (R1991).

Hex Head and Hex Washer Head

Wrench-driven fastening for high torque.

The hex head machine screw has a flat or indented top surface with six flat sides and a flat bearing surface. Available in both regular and large head sizes. Unless otherwise specified, hex head machine screws are not slotted.

The hex washer head adds an integral flat washer that projects beyond the hex sides, providing a wider bearing surface. Both slotted hex heads and slotted hex washer heads are not recommended for new designs because the slotting operation creates burrs that interfere with wrench engagement.

Hex Head Dimensions (Regular Head):

Nom. Size Basic Dia. Width Across Flats (Max) Width Across Flats (Min) Across Corners (Min) Head Height (Max) Head Height (Min)
#1 0.0730 0.125 0.120 0.134 0.044 0.036
#4 0.1120 0.188 0.181 0.202 0.060 0.049
#6 0.1380 0.250 0.244 0.272 0.093 0.080
#8 0.1640 0.250 0.244 0.272 0.110 0.096
#10 0.1900 0.312 0.305 0.340 0.120 0.105
1/4 0.2500 0.375 0.367 0.409 0.190 0.172
5/16 0.3125 0.500 0.489 0.545 0.230 0.208
3/8 0.3750 0.562 0.551 0.614 0.295 0.270

All dimensions in inches per ANSI B18.6.3-1972 (R1991).

Hex Washer Head Dimensions:

Nom. Size Basic Dia. Across Flats (Max) Across Corners (Min) Head Ht. (Max) Washer Dia. (Max) Washer Thick. (Max)
#4 0.1120 0.188 0.202 0.060 0.243 0.019
#6 0.1380 0.250 0.272 0.093 0.328 0.025
#8 0.1640 0.250 0.272 0.110 0.348 0.031
#10 0.1900 0.312 0.340 0.120 0.414 0.031
1/4 0.2500 0.375 0.409 0.190 0.520 0.050
3/8 0.3750 0.562 0.614 0.295 0.780 0.063

All dimensions in inches per ANSI B18.6.3-1972 (R1991).

Round Head (Obsolescent)

Not recommended for new designs. Use pan head instead.

The round head has a semi-elliptical top surface and a flat bearing surface. Due to the superior driving characteristics and dimensional overlap of the pan head, the round head is being phased out of new engineering standards.

If you encounter round head machine screws in legacy equipment, replace with pan head equivalents during maintenance upgrades where form-fit-function allows.

the practitioner's Notebook: The Head Type Decision Matrix

After the 3 AM incident, the practitioner created a decision framework she taped to her monitor. Here's the expanded version:

Design Requirement Recommended Head Type Why
Flush surface required Flat Countersunk (82°) Sits completely flush in countersunk hole
Flush with wider bearing Flat Countersunk (100°) Shallower cone, more bearing area
General purpose, protruding OK Pan Head Best all-around: good drive, good bearing
Maximum torque resistance Fillister Head Deep slot, cylindrical sides resist cam-out
Decorative with countersink Oval Countersunk Elegant dome above flush countersink
Wire/cable clamping Binding Head Undercut shoulder captures wires
Thin material, wide bearing Truss Head Widest head diameter per screw size
Wrench-driven, high torque Hex Head Six-sided for socket or wrench engagement
Wrench + bearing area Hex Washer Head Integral washer distributes load
Lockwire required (aerospace) Drilled Fillister Cross-drilled hole for safety wire

Machine Screw Nuts: Square and Hexagon

Every machine screw that doesn't go into a tapped hole needs a nut. The standard defines two types:

  • Hexagon nuts have flat, chamfered tops. The top circle diameter should be the maximum width across flats within a tolerance of minus 15%.
  • Square nuts have flat tops and bottoms without chamfer. Square nuts are only available with UNC Class 2B threads.
Nom. Size Basic Dia. Width Across Flats (Basic) Hex: Across Flats (Max) Hex: Across Corners (Max) Square: Across Corners (Max) Thickness (Max) Thickness (Min)
#0 0.0600 5/32 0.156 0.221 0.180 0.050 0.043
#2 0.0860 3/16 0.188 0.265 0.217 0.066 0.057
#4 0.1120 1/4 0.250 0.354 0.289 0.098 0.087
#6 0.1380 5/16 0.312 0.442 0.361 0.114 0.102
#8 0.1640 11/32 0.344 0.486 0.397 0.130 0.117
#10 0.1900 3/8 0.375 0.530 0.433 0.130 0.117
#12 0.2160 7/16 0.438 0.619 0.505 0.161 0.148
1/4 0.2500 7/16 0.438 0.619 0.505 0.193 0.178
5/16 0.3125 9/16 0.562 0.795 0.650 0.225 0.208
3/8 0.3750 5/8 0.625 0.884 0.722 0.257 0.239

All dimensions in inches per ANSI B18.6.3-1972 (R1991).

Cross Recesses: Types I, IA, II, and III

Slotted heads are just the beginning. Four cross recess types can be used in lieu of slots:

  • Type I (Phillips): Large center opening, tapered wings, blunt bottom, relieved edges
  • Type IA (Phillips modified): Similar to Type I with slight variations for improved engagement
  • Type II (Pozidriv): Designed to reduce cam-out tendency at high torque
  • Type III (Square/Robertson): Square center recess providing positive engagement with virtually zero cam-out

Cross recess dimensions (diameter M, width N, and depth T) together with penetration gaging depths are defined in ANSI B18.6.3-1972 (R1991) for inch-series screws and ANSI/ASME B18.6.7M-1985 for metric machine screws.

Thread Length Rules: The Hidden Specification

This is one of the most commonly overlooked machine screw specifications—and it directly affects your assembly's thread engagement, clamping force, and reliability.

Inch-Series Thread Lengths (ANSI B18.6.3)

The rules differ based on screw size:

For sizes #5 and smaller:

  • Nominal lengths equal to 3 diameters and shorter: Full form threads extend to within 1 pitch of the head bearing surface (or closer)
  • Nominal lengths greater than 3 diameters, up to 1-1/8 in.: Full form threads extend to within 2 pitches of the head bearing surface (or closer)
  • Longer than 1-1/8 in.: Minimum full form thread length of 1.00 inch unless otherwise specified

For sizes #6 and larger:

  • Nominal lengths equal to 3 diameters and shorter: Full form threads extend to within 1 pitch of the head bearing surface (or closer)
  • Nominal lengths greater than 3 diameters, up to 2 inches: Full form threads extend to within 2 pitches of the head bearing surface (or closer)
  • Longer than 2 inches: Minimum full form thread length of 1.50 inches unless otherwise specified

Metric Thread Lengths (ANSI/ASME B18.6.7M)

Metric machine screws follow a different structure, with minimum thread lengths defined per screw size and head style. The following table shows the minimum full-form thread length (B) for pan, hex, and hex flange head screws when the nominal screw length exceeds the threshold:

Screw Size & Pitch Threshold Length Min. Thread Length (B)
M2 × 0.4 — Threaded to head for shorter lengths
M2.5 × 0.45 — Threaded to head for shorter lengths
M3 × 0.5 — Threaded to head for shorter lengths
M4 × 0.7 — Defined per standard tables
M5 × 0.8 — Defined per standard tables
M6 × 1 — Defined per standard tables
M8 × 1.25 — Defined per standard tables
M10 × 1.5 — Defined per standard tables

Length tolerances for metric machine screws:

Nominal Length Range Tolerance
Up to 3 mm, inclusive ± 0.2 mm
Over 3 to 10 mm, inclusive ± 0.3 mm
Over 10 to 16 mm, inclusive ± 0.4 mm
Over 16 to 50 mm, inclusive ± 0.5 mm
Over 50 mm ± 1.0 mm

ANSI Metric Machine Screws (ANSI/ASME B18.6.7M-1985)

This is where the engineering world bridges the inch-metric divide. Standard B18.6.7M covers metric flat and oval countersunk, slotted and recessed pan head, hex head, and hex flange head machine screws.

Threads

Metric machine screws use coarse M profile threads as given in ANSI B1.13M, unless otherwise specified. The tolerance class is 6g for plain finish screws or bolts and for plated/coated screws before plating.

Designation Format

Metric machine screws are designated in this sequence:

Nominal size × Thread pitch × Nominal length — Product name, including head type and driving provision; header point if desired; material (including property class if steel); protective finish if required.

Examples:

  • M8 × 1.25 × 30 Slotted Pan Head Machine Screw, Class 4.8 Steel, Zinc Plated
  • M3.5 × 0.6 × 20 Type IA Cross Recessed Oval Countersunk Head Machine Screw, Header Point, Brass

ISO convention: It is common practice to omit the thread pitch when using the metric coarse thread series. For example, M10 stands for M10 × 1.5.

Metric Pan Head Dimensions

Screw Size & Pitch Body Dia. (Max) Body Dia. (Min) Head Dia. (Max) Head Dia. (Min) Head Ht. Slotted (Max) Head Ht. Slotted (Min) Head Ht. Recessed (Max) Head Ht. Recessed (Min) Slot Width (Max) Slot Depth (Min)
M2 × 0.4 2.00 1.65 4.0 3.7 1.3 1.1 1.6 1.4 0.7 0.4
M2.5 × 0.45 2.50 2.12 5.0 4.7 1.5 1.3 2.1 1.9 0.8 0.5
M3 × 0.5 3.00 2.58 5.6 5.3 1.8 1.6 2.4 2.2 1.0 0.7
M3.5 × 0.6 3.50 3.00 7.0 6.6 2.1 1.9 2.6 2.3 1.2 0.8
M4 × 0.7 4.00 3.43 8.0 7.6 2.4 2.2 3.1 2.8 1.5 0.9
M5 × 0.8 5.00 4.36 9.5 9.1 3.0 2.7 3.7 3.4 1.5 1.2
M6 × 1 6.00 5.21 12.0 11.5 3.6 3.3 4.6 4.3 1.9 1.4
M8 × 1.25 8.00 7.04 16.0 15.5 4.8 4.5 6.0 5.6 2.3 1.9
M10 × 1.5 10.00 8.86 20.0 19.4 6.0 5.7 7.5 7.1 2.8 2.4

All dimensions in millimeters per ANSI/ASME B18.6.7M-1985.

Metric Flat Countersunk Head Dimensions

Screw Size & Pitch Body Dia. (Max) Head Dia. Theor. Sharp (Max) Head Dia. Actual (Min) Head Ht. (Max) Fillet Radius (Min) Slot Width (Max) Slot Depth (Max)
M2 × 0.4 2.00 4.4 3.5 1.2 0.4 0.7 0.6
M2.5 × 0.45 2.50 5.5 4.4 1.5 0.5 0.8 0.7
M3 × 0.5 3.00 6.3 5.2 1.7 0.6 1.0 0.9
M4 × 0.7 4.00 9.4 8.0 2.7 0.8 1.5 1.3
M5 × 0.8 5.00 10.4 8.9 2.7 1.0 1.5 1.4
M6 × 1 6.00 12.6 10.9 3.3 1.2 1.9 1.6
M8 × 1.25 8.00 17.3 15.4 4.6 1.6 2.3 2.3
M10 × 1.5 10.00 20.0 17.8 5.0 2.0 2.8 2.6

All dimensions in millimeters per ANSI/ASME B18.6.7M-1985.

Engineering use and verification

Begin with load paths, motion, interfaces and credible failure modes. Define duty cycle, environment, alignment, lubrication, manufacturing variation and maintenance access before choosing a component. Check static strength, fatigue, stiffness, heat, wear and fastening together because improving one constraint can worsen another. Record assumptions and verify the assembled system, not just catalogue ratings for isolated parts.

  • Confirm scope, assumptions, interfaces and required outcome.
  • Use one controlled unit system and show every conversion.
  • Identify current project, customer and regulatory requirements.
  • Separate source examples from mandatory acceptance criteria.
  • Check calculations, tables and selections by an independent method.
  • Verify safety, maintainability and credible failure modes.
  • Record evidence, revisions, approvals and unresolved limitations.
  • Validate the result under representative operating conditions.
Machine Screws, Cap Screws and Set Screws: BS 4183 Machine Screw Nuts (Metric, Pressed Type) Machine Screws, Cap Screws and Set Screws — Part 4 Machine Screws, Cap Screws and Set Screws: Metric Hex and Hex Flange Head Dimensions

Internal links use extensionless KEVOS routes. The CMS supplies the site navigation, article reader and search interface.

Continue learning

Machine Screws, Cap Screws and Set Screws — Part 4Guide · Machine DesignNEXT LESSON →Machine Screws, Cap Screws and Set Screws: Metric Hex and Hex Flange Head DimensionsGuide · Machine DesignMachine Screws, Cap Screws and Set Screws: BS 4183 Machine Screw Nuts (Metric, Pressed Type)Guide · Machine DesignSelf-Threading Screws, Thread Inserts and Hole Design: Every Type, Every Thread, Every ApplicationGuide · Machine Design