Complete Guide to Reading Bolt and Nut Size Tables

For those of you involved in the automotive world, understanding the sizes of bolts, nuts, and screws is crucial. These three components play an important role in joining various parts of a vehicle with precision.

However, many people find it difficult to read the complete size tables for bolts and nuts. This article will help you better understand bolt sizes, so you can choose them correctly according to your needs.

Understanding What Bolts, Nuts, and Screws Are

Bolts, nuts, and screws are components that serve as connectors between several vehicle parts.

In addition, these two tools can also be easily removed without causing any risk of damage.

Although they look similar, these three components actually consist of several sizes and are presented in a special table.

Sizes of Nuts and Bolts

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Before understanding how to read the size table for nuts and bolts correctly, it is best to recognize each part along with its specifications.

By recognizing each part of the tool, it indirectly helps you know what the standard size used is.

So, what parts does a bolt have?

1. B (width across flats).

2. Length (L).

3. Thread length (TL).

4. Pitch (P).

Diameter (D). Width Across Flats is the part of the bolt head that is wide but parallel, which has a size similar to the size of the wrench to open and tighten the bolt.

Length is the total length of the bolt, while Thread Length is the length of the bolt's thread. Pitch is the distance between the peaks of the thread from one to another.

Meanwhile, the diameter of the bolt thread is used as a marker and the size code of the bolt.

Nut Table

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After understanding each part of the bolt, it is now time to know the size of the bolt nut and the standards.

Why is it necessary to know the standard bolt sizes? Because each country has different standard bolt sizes, including Indonesia.

However, in the automotive industry, there are at least two standards that are often used. These two bolt standards consist of metric-sized bolts (millimeters) and Whitworth-sized bolts (inches).

Measurement Based on ISO Metric Standards

Specifically for metric-sized bolts (ISO Metric), this is a bolt size that is widely applied in various countries. The ISO Metric size standard has several characteristics, namely its unit of measurement uses millimeters.

The angle between the pitches is about 60 degrees, and it is symbolized by the letter “M,” which stands for Metric. It is not too difficult to read the complete size table for bolts and nuts, as you only need to know the code provided.

For example, when you find a code that reads “M8x1.5 2 LH L:35mm,” this code means that the bolt uses the metric standard due to the presence of the “M” symbol at the beginning of the code.

The number 8 after the letter “M” indicates the size of the bolt thread diameter, which is 8mm. The code showing the number 1.25 means the pitch or thread distance is 1.25mm.

The number 2 in the code indicates the material class number 2, and LH indicates the left-hand thread direction. Then the code L:35 means the length of the bolt.

Measuring Nuts and Bolts

To determine the size of the bolt nut, there are several steps that need to be taken.

First, measure the width of the bolt head using a caliper or known as a vernier caliper. The size of the bolt head will determine how large the wrench size is to tighten or loosen the bolt.

Then you need to measure the pitch using a thread pitch gauge by aligning it parallel to the bolt thread. If the installation is not parallel, there is a risk of measurement error.

The next step is to measure the length of the bolt using a caliper.

Although it seems simple, measuring the length of the bolt cannot be done carelessly. Because in this measurement, you only need to know the length of the bolt thread.

To ensure accurate measurement, you need to match the length of the old bolt thread with the bolt you intend to buy at the nearest automotive store.

The whitworth bolt standard also has several characteristics in its bolt code. Some of these characteristics include its unit of measurement using inches, the angle between pitches is around 55 degrees, and it is symbolized by the letter “W,” which stands for Whitworth size.

So how do you read the code on the bolt?

For example, when you find a bolt code that reads W 3/8” x 16, the way to read it is that the letter “W” is interpreted as the whitworth size.

Meanwhile, the number 3/8” indicates that the diameter of the bolt thread reaches 3/8 inches or approximately 0.375 inches. The number “16” in the code means the number of pitches present in 1 inch is about 16.

Sizes of Screws and How to Read Them

Screws have size codes similar to bolts. For example, the code 6 x 3/4” means:

6: The diameter size of the screw from the head to the shaft.

3/4”: The length of the screw in inches.

Knowing how to read the sizes of bolts, nuts, and screws is very important to ensure compatibility with vehicle components. Errors in selecting sizes can cause bolts or screws to not be used optimally.

If the sizes of the bolts and screws purchased do not match the available holes, of course, the tools cannot be used to join several vehicle components.