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Screws

Most people know what a screw is, but some might not know what sets them apart from bolts. Unlike bolts, screws are designed to be tightened or loosened by the head of the fastener instead of the nut. A screw is simply an externally threaded fastener designed to be tightened or loosened by torquing the head. Sometimes a nut is used with a screw but sometimes the screw threads directly into wood, steel or plastic. No matter the project, there’s likely a specific screw made for your use case.

Machine Screws
Self-Tapping Screws
Self-Drilling Screws
Thread-Forming Screws

Machine Screws

Machine screws typically have a diameter of 1/4″ or less. They’re fully threaded, which allows them to be screwed into pre-tapped holes or used with a nut. Machine screws are available in several head styles and drive types to fit a variety of projects.

Learn more about some of the most common head styles below.

Pan

Pan-head machine screws feature slightly domed heads with flat bearing surfaces. It’s a great general-purpose screw due to its bearing area, and comes in several drives, including:

  • Phillips
  • Slotted
  • Combo
  • Six-lobe

Pan Head ASME B18.6.3

Several pan screws
Head Diameter Head Height Slotted Head Height Phillips/Torx
Screw Size Max Min Max Min Max Min
2 0.167 0.155 0.053 0.045 0.062 0.053
3 0.193 0.180 0.060 0.051 0.071 0.062
4 0.219 0.205 0.068 0.058 0.080 0.070
5 0.245 0.231 0.075 0.065 0.089 0.079
6 0.270 0.256 0.082 0.072 0.097 0.087
8 0.322 0.306 0.096 0.085 0.115 0.105
10 0.373 0.357 0.110 0.099 0.133 0.122
12 0.425 0.407 0.125 0.112 0.151 0.139
1/4 (14) 0.492 0.473 0.144 0.130 0.175 0.162

Round

Roundhead machine screws have semi-elliptical top surfaces and flat bearing surfaces. This design is ideal for applications where the screw head is intended to be visible in the final assembly. 

These screws typically come in the following drives:

  • Phillips
  • Slotted
  • Combo
A round screw

Round ASME B18.6.3

Head Diameter Head Height
Screw Size Max Min Max Min
2 0.162 0.146 0.069 0.059
3 0.187 0.169 0.078 0.067
4 0.211 0.193 0.086 0.075
5 0.236 0.217 0.095 0.083
6 0.260 0.240 0.103 0.091
8 0.309 0.287 0.120 0.107
10 0.359 0.335 0.137 0.123
12 0.408 0.382 0.153 0.139
1/4 (14) 0.472 0.443 0.175 0.160

Truss

Truss-head machine screws feature low-profile, rounded heads with large bearing surfaces, especially when compared to other head styles. They are a great choice where a flush or low-profile finish is desired and a large contact area is needed.

Typical drives include:

  • Phillips
  • Slotted
The top and side of a truss screw
Truss ASME B18.6.3
Head Diameter Head Height
Screw Size Max Min Max Min
2 0.194 0.180 0.053 0.044
3 0.226 0.211 0.061 0.051
4 0.257 0.241 0.069 0.059
5 0.289 0.272 0.078 0.066
6 0.321 0.303 0.087 0.074
8 0.384 0.364 0.102 0.088
10 0.448 0.425 0.118 0.103
12 0.511 0.487 0.134 0.118
1/4 (14) 0.573 0.546 0.150 0.133

Flat

Flat-head machine screws have 82° countersunk heads with flat tops and cone-shaped bearing surfaces. They’re used when the fastener must not protrude beyond its mating surface.

Common drives include:

  • Phillips
  • Slotted
  • Six-lobe
A flat screw
Flat ASME B18.6.3
Head Diameter Head Height
Screw Size Max Min Max Min
2 0.162 0.144 0.051 0.040
3 0.187 0.167 0.059 0.047
4 0.212 0.191 0.067 0.055
5 0.237 0.215 0.075 0.062
6 0.262 0.238 0.083 0.069
8 0.312 0.285 0.100 0.084
10 0.362 0.333 0.116 0.098
12 0.412 0.380 0.132 0.112
1/4 (14) 0.477 0.442 0.153 0.131
An oval screw

Oval

Oval-head machine screws feature countersunk heads with rounded top surfaces and cone-shaped, 82° bearing surfaces. This design makes them ideal to use in place of flat-head machine screws when the design calls for a more decorative finish.

Typical drives include:

  • Phillips
  • Slotted
Oval ASME B18.6.3
Head Diameter
Screw Size Max Min Head Crown Height Ref Total Head Height Ref
2 0.162 0.144 0.051 0.080
3 0.187 0.167 0.059 0.092
4 0.212 0.191 0.067 0.104
5 0.237 0.215 0.075 0.116
6 0.262 0.238 0.083 0.128
8 0.312 0.285 0.100 0.152
10 0.362 0.333 0.116 0.176
12 0.412 0.380 0.132 0.200
1/4 (14) 0.477 0.442 0.153 0.232

Hex

Hex head machine screws are designed to be tightened or loosened with a wrench or socket. They’re commonly used in industrial applications where high torque and secure fastening are essential.

The most common drive for these screws is:

  • Hex
The top and side of a hex screw
Hex ASME B18.6.3
Head Diameter Head Height
Screw Size Max Min Max Min
2 0.125 0.120 0.050 0.040
4 0.188 0.181 0.060 0.049
5 0.188 0.181 0.070 0.058
6 0.250 0.244 0.093 0.080
8 0.250 0.244 0.110 0.096
10 0.312 0.305 0.120 0.105
12 0.312 0.305 0.155 0.139
1/4 (14) 0.375 0.367 0.190 0.017

Hex Washer Head

Hex washer head screws have a hex head with built-in washer. The washer face provides a larger bearing surface than a standard hex head screw. They are commonly used in applications where a flat bearing surface is advantageous.

A hex washer head screw
Hex Washer Head ASME B18.6.3
Head Diameter Head Height Washer Dia. Washer Thick.
Screw Size Max Min Max Min Max Min Max Min
2 0.125 0.120 0.050 0.040 0.166 0.154 0.016 0.010
4 0.188 0.181 0.060 0.049 0.243 0.225 0.019 0.011
5 0.188 0.181 0.070 0.058 0.260 0.240 0.025 0.015
6 0.250 0.244 0.093 0.080 0.328 0.302 0.025 0.015
8 0.250 0.244 0.110 0.096 0.348 0.322 0.031 0.019
10 0.312 0.305 0.120 0.105 0.414 0.384 0.031 0.019
12 0.312 0.305 0.155 0.139 0.432 0.398 0.039 0.022
1/4 (14) 0.375 0.367 0.190 0.017 0.520 0.480 0.050 0.030

Self-Tapping Screws

Self-tapping screws, also known as sheet metal screws, are designed to create their own threads as they’re driven into a material like sheet metal. Just like machine screws, self-tapping screws are available in various head styles and drives. However, they also come with different points, type A being the most common.

Type A

Type A self-tapping screws have widely spaced threads and gimlet points. Their coarse threads and sharp point make them easy to tell apart from other types of screws. Type A are commonly used to create threads in sheet metal, wood, and other thin materials. 

A type-A screw
Type A
D refers to the D Major diameter of a Type A screw while lowercase d refers to the d major diameter.
Type A Self Tapping Screw

Type A Self Tapping Screw ASME B18.6.3

D Major Diameter d Major Diameter
Size Threads Per Inch Max Min Max Min Suggested Hole Size
6 0.138 18 0.141 0.136 0.102 0.096 0.1160
8 0.164 15 0.168 0.162 0.123 0.116 0.1360
10 0.190 12 0.194 0.188 0.133 0.126 0.1590
12 0.216 11 0.221 0.215 0.162 0.155 0.1875
14 0.250 10 0.254 0.248 0.185 0.178 0.2165
Tolerance on Length Up to 1" Inc.: +/- 0.03 Over 1": +/- 0.05

Type AB

Type AB self-tapping screws have gimlet points and finer threads than type A. These fine threads make Type AB ideal for thinner or more brittle materials, even if type A is the most commonly used solution.

A type AB screw
Type AB
D refers to the D Major diameter of a Type AB screw while lowercase d refers to the d major diameter.
Type AB Self Tapping Screw

Type AB Self Tapping Screw ASME B18.6.3

D Major Diameter d Major Diameter
Size Threads Per Inch Max Min Max Min Suggested Hole Size
2 0.086 32 0.088 0.082 0.064 0.060 0.0760
3 0.099 28 0.101 0.095 0.075 0.071 0.0810
4 0.112 24 0.114 0.108 0.086 0.082 0.0860
5 0.125 20 0.130 0.123 0.094 0.090 0.1065
6 0.138 20 0.139 0.132 0.104 0.099 0.1160
8 0.164 18 0.166 0.159 0.122 0.116 0.1360
10 0.190 16 0.189 0.182 0.141 0.135 0.1590
12 0.216 14 0.215 0.208 0.164 0.157 0.1875
14 0.250 14 0.246 0.237 0.192 0.185 0.2165
Tolerance on Length Up to 1" Inc.: +/- 0.03 Over 1": +/- 0.05

Type B

Type B self-tapping screws feature a finer thread like type AB, but they’re set apart by their blunt points. This blunted end helps prevent damage, especially when working with softer or more brittle materials.

A type B screw
Type B
D refers to the D Major diameter of a Type B screw while lowercase d refers to the d major diameter.
Type B Self Tapping Screw

Type B Self Tapping Screw ASME B18.6.3

D Major Diameter d Major Diameter P Point Diameter S Point Length
Size Threads Per Inch Max Min Max Min Max Min Max Min
2 0.086 32 0.088 0.082 0.064 0.060 0.058 0.054 0.062 0.047
3 0.099 28 0.101 0.095 0.075 0.071 0.068 0.064 0.071 0.054
4 0.112 24 0.114 0.108 0.086 0.082 0.079 0.074 0.083 0.063
5 0.125 20 0.130 0.123 0.094 0.090 0.087 0.082 0.105 0.075
6 0.138 20 0.139 0.132 0.104 0.099 0.095 0.089 0.105 0.075
8 0.164 18 0.166 0.159 0.122 0.116 0.112 0.106 0.113 0.083
10 0.190 16 0.189 0.182 0.141 0.135 0.130 0.123 0.125 0.094
12 0.216 14 0.215 0.208 0.164 0.157 0.152 0.145 0.143 0.107
14 0.250 14 0.246 0.237 0.192 0.185 0.179 0.171 0.143 0.107
Tolerance on Length Up to 3/4" Inc.: - 0.03 Over 3/4 to 1-1/2" Incl: -0.05 Over 1-1/2": -0.06

Self-Drilling Screws

Self-drilling screws combine drilling and fastening into a single step while eliminating the need for a pilot hole. These screws feature a drill-shaped point that can bore through materials while the screw is driven in. The threads then help create a secure connection.

Key Characteristics & Advantages 

  • Faster installation: Self-drilling screws eliminate the need for pre-drilling, which saves time.
  • Less hardware: The design eliminates the need for a separate drill bit.
  • Versatile: These screws are suitable for a wide range of materials and applications.
  • Cost-savings: Because they speed up installation and reduce the need for additional hardware, in many cases, self-drilling screws can reduce overall project costs.

Self-drilling screws come in a variety of head styles, drill points, and materials. Marshall Sales proudly offers Strong-Point® self-drilling screws. You can find more information on the available varieties in their catalog here.

The drill bit on the end of a self-drilling screw

Thread-Forming Screws

Thread-forming screws feature threads that displace material outward when they’re drilled in, which creates an internal thread. This process avoids the removal of material. The resulting thread is usually stronger and more resistant to loosening from vibration.

Taptite® (Thread-Rolling) and Plastite® (48-2 Thread Forming) are the most common thread-forming screws on the market. They have a unique trilobular thread shape that displaces the material to form around the screw, which creates a strong, vibration-resistant connection.

It’s common to find thread-forming screws used in industries like automotive, electronics, and appliances, especially when joining softer materials like plastics and sheet metal.

A diagram of a thread-forming screw

Taptite® Thread Rolling

Taptite® or thread-rolling screws feature machine screw threads and are available in both inch and metric diameters. The variety of different head types come in steel and stainless steel.

Key Characteristics & Advantages 

  • Strong bonds: The design of these screws generates strong mating threads.
  • Reduced failure: Thread-rolling screws minimize radial stress and reduce boss failure.
  • Tight tolerance: The sleek design allows for tight dimensional tolerance.
  • Consistency: Each screw offers a consistent thread profile with other Taptite® screws.
  • Reduced costs: Since there’s no need for pre-tapping, using Taptite® screws can reduce assembly costs.
  • Vibration resistant: The unique design resists vibration loosening.

Taptite® Thread Rolling

* 2-3 Pitch Lead Length

G refers to the diameter of a Taptite Thread Rolling screw, while D refers to the width. C is the maximum width.
C D G
Screw Size Max Min Max Min
2-56 0.088 0.084 0.084 0.080 0.070
3-48 0.101 0.097 0.097 0.093 0.081
4-40 0.115 0.111 0.110 0.106 0.090
6-32 0.141 0.135 0.135 0.129 0.111
8-32 0.167 0.161 0.161 0.155 0.137
10-24 0.194 0.188 0.186 0.180 0.153
10-32 0.193 0.187 0.187 0.181 0.163
1/4-20 0.255 0.249 0.245 0.239 0.221
5/16-18 0.318 0.312 0.307 0.301 0.264
3/8-16 0.381 0.375 0.369 0.363 0.320
Tolerance on Length Thru 3/4" Over 3/4" Over 1.5"
-0.030 -0.050 -0.060
A diagram of a Plastite screw

Plastite® (48-2)

Plastite®, also known as 48-2 screws, have a similar thread pattern to self-tapping screws. However, they also feature a narrow thread profile that maximizes performance when used with thermoplastics.

Key Characteristics & Advantages 

  • Reduced stress: The trilobular thread shape reduces radial stress.
  • Increased shear area: The steep angle of the helix creates a greater shear area than other types of screws.
  • Reduced failure: Thread-rolling screws minimize radial stress and reduce boss failure.
  • Increased reliability: The considerable consistency of these screws means you can count on them to be high quality each and every time.
  • Less hardware: The design of Plastite® screws eliminates the need for inserts and lock washers.
  • Reduced costs: Since these screws don’t require inserts and lock washers, they can help reduce assembly costs overall.

Plasite® 48-2 Thread Rolling Screw

C D Recommended Pilot Hole
Screw Size Max Min Max Min Soft Ductile Brittle
2-28 0.092 0.086 0.089 0.083 0.076 0.080
3-24 0.110 0.104 0.106 0.100 0.088 0.094
4-20 0.127 0.121 0.123 0.117 0.100 0.106
6-19 0.147 0.141 0.143 0.137 0.122 0.128
8-16 0.185 0.179 0.179 0.173 0.149 0.158
10-14 0.212 0.206 0.208 0.202 0.175 0.185
12-11 0.232 0.226 0.226 0.220 0.195 0.205
1/4-10 0.276 0.270 0.268 0.262 0.224 0.240
Tolerance on Length Thru 3/4" Over 3/4"
+/- 0.030" +/- 0.050""
Ready to Choose the Correct Screw?

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