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What Information Should a Flange Bolt Chart Include?

A proper flange connection is not complete without a suitable bolt. Flange bolts come in different types and sizes, and selecting the most appropriate for your next project can be a daunting task. 

While a flange bolt chart provides you with the sizes, diameters, and lengths of different bolts. These are not the only factors needed when selecting a bolt that meets your standards. 

Read on to find out the most critical information you need before settling for a bolt that matches your specifications.

How to Select the Right Type of Bolt

Flange bolts can be used on irregular and oversized holes because of the washer heads and large contact area that evenly spread the clamping force. Before choosing a flange bolt that matches your needs, you'll need to consider the following.


The threading requirement for bolts depends on the size and length. Flange bolts are threaded either partially or fully. An ideal flange bolt should be long enough to guarantee the thread is in complete contact with the nut. 

This is achieved when two or more flange bolt threads extend past the nut after being tightened. Ideally, two full threads should be visible on the nut's topside for a tight grip.

Type of Bolt

Flange bolts are classified into four types: Hex, 12 Point, Serrated Hex and Metric Flange Bolts.

Hex flange bolts feature an integrated washer head and are commonly used on motor frames.

Grade G flange lock nuts are used primarily with hex flange bolts to ensure proper tightening. Twelve-point flange bolts, also known as ferry bolts, are the alternative for hex socket cap screws. They are commonly used in aircraft to hold the outer casing firmly and in automotive since installation with a 12 point socket is easy.

Material Type and Grade

Your bolt material should be able to meet your project needs in terms of hardness, yield strength, and chemical composition. Think about the greatest amount of tensile load the bolt will be able to handle. 

Tensile load is calculated by multiplying the tensile strength with the area of the load material. High tensile loads are dangerous because they can lead to fasteners' deformity. Additionally, your flange bolt material should be hard enough to withstand wearing, depression, and corrosion.

The fastener should be resilient with excellent ductility. An effective flange bolt has a lower yield strength to minimum tensile strength ratio.

Size of the Bolt, Diameter, and Length

The flange bolt size is determined by the flange head bearing size. When utilizing a graded flange bolt, it is critical to use a nut that is either the same as or one grade higher than the bolt. 

The size, diameter, and length are listed on the flange bolt chart. The hex size ranges from 3/8" to 3/4" with a length of 1" to 5", while the serrated hex ranges from 1/4" to 1" with a length of 3/8" to 2 1/2" and the 12 point flange bolt ranges from 1/2" to 7" with a length of 1/2" to 7".

Manufacturers and Industry Standards

Before selecting a suitable bolt, it's crucial to consider the manufacturer's recommendations, the industry, and its use case. Flange bolts are different, and every company has its own bolting standards regarding lubrication, bolt reuse recommendations, and torque tightening procedures.

Torque value depends on the present friction between the head of the nut and bolt threads which is affected by thread lubrication. Torque values are specified on the bolt chart and should range between 40 to 70 percent of the bolt's strength limit. From the industrial fastening standards, you'll be able to determine if a suggested torque value belongs to dry or lubricated thread.

Contact Big Bolt for Quality Fasteners

When it comes to finding quality fasteners, partnering with a company with experts who understand the most critical information is a must. It helps to save you time when you’re in the process of choosing the most appropriate fastener for your project. 

Big Bolt manufactures quality bolts and nuts, with a quick turnaround time to ensure efficiency in your project. Contact us today to get quality flange bolts that meet your specifications.

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