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Explaining Screw and Nail Sizes

Widespread fastener use has benefited in modern times from standardization focused on preventing misuse and encouraging compatibility. Organizations such as the Industrial Fastener Institute and federal legislation like the Fastener Quality Act have worked to promote stringent and wide-ranging standards for fasteners of all kinds. Nails, screws, bolts, clamps, rivets and other fasteners are all governed by these standards, allowing manufacturers, engineers, wood-workers and others to produce materials that can work using these regulated measurements and compositions. Nails and screws, possibly the most commonly used fasteners, both benefit from standardization tables, but the uninitiated might have trouble determining what sizes are good for their projects.

Nails – Standard Measurements 

This chart illustrates industry-standards for size measurements.

This chart shows the standard nail sizes and their dimensions. Under “nail size,” the “penny size” refers to a standard nail unit. Nails are measured in pennies, believed to be from older times when nails were sold by the penny. At the time, the abbreviation for pennies was d, so nail sizes are described as 2D, 3D, etc. The shank diameter and length refer to the shaft part of the nail, called the shaft, which is driven into the surface. The head is, of course, the top portion struck to drive the nail into the material.

Nail Size
 
Shank Diameter
Shank Length
Head Diameter
Penny Size
Guage
Nominal
Nominal
Apprx.
2D
15
0.072
1"
3/16"
 
14
0.083
1"
13/64"
3D
14
0.083
1.25"
13/64"
4D
12
0.109
1.5"
1/4"
5D
12
0.109
1.75"
1/4"
6D
11
0.12
2"
17/64"
8D
10
0.134
2.5"
9/32"
10D
9
0.148
3"
5/16"
12D
9
0.148
3.25"
5/16"
16D
8
0.165
3.5"
11/32"
20D
6
0.203
4"
13/32"
30D
5
0.22
4.5"
7/16"
40D
4
0.238
5"
15/32"
60D
4
0.238
6"
17/32"
 
2
0.284
6"
17/32"



Screws – Standard Measurements

Screw measurements are slightly more complex than nails, because there are more variables in their fabrication and usage. These include drive type, thread size, and the many different shank and head sizes.

Screw Drive Types

There are numerous thread sizes. Some are more common while others are used only in very specific applications or in certain countries. These drive types include:

  • Slotted, also called flathead, drive types are a simple slotted groove across the entire head of the screw.

  • Phillips head screws are a simple perpendicular cross groove connected at the center of the screw head.

  • Tri-Wing screws are present in many electronics applications, like video game consoles and cellular phones. They are a three-pronged groove connected at the center of the screw head.

  • Triple Square screws are common in German automotive applications. The name is meant as a literal description, as the groove consists of three square shapes overlaid upon one another, each rotated fifteen degrees from the other two.

  • Polydrive screws are also common in the automotive industry. It features a hexagonal shape, with each angle butting out into a larger tooth.

  • Spline drive is similar to the triple square, but features in different sizes.

  • Double hex is also similar to triple square, but with more obtuse angles.

Screw Thread Measurements

In terms of consistency, screw thread types are wide-ranging, which can lead to incompatibility. The International Organization for Standardization (ISO) has one system which is slowly gaining more widespread acceptance, leading to more standardization and wider compatibility settings.

There are too many differentiations to enumerate them all here, but the basic system of ISO measurement is as follows: Because ISO thread standards are metric, they are demarcated as M followed by the nominal diameter, in millimeters. If the pitch of the thread is nonstandard, this diameter is followed by an “x” and the pitch. If a standard pitch is used, no pitch is mentioned.

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