How to Identify High Tensile Bolts

Here’s how you can determine the correct bolt to use for your application.
high tensile bolt

(Taken from this post by Champion Parts. Republished with permission. Edited for point of view and relevance.)

High tensile bolts are used in applications where durability is critical to firmly and safely hold components together.  

A common example would be in an automotive system, where high tensile bolts:

  1. Hold together the linkages of the suspension system; or
  2. Attach the brake calipers to the knuckles

Getting this right is important for obvious reasons: safety, reliability and the longevity of components. 

This excerpt from Champion Parts might point you in the right direction. 

Disclaimer: AIMS is not an expert in fastener design, therefore the information provided herein should not be treated as professional advice. The official source is cited.

 

Read the head markings

The markings on the head face of a bolt can be confusing. How do we specify the grades between each pattern and make sure you get the correct size? 

1. Check if there are any head markings. They will indicate if the bolt is metric or imperial and the grade/class.

bolt head markings

 

2. Look at the threaded part of the bolt/setscrew and identify if it is a fine thread or coarse thread. Using a vernier, measure the diameter of the threaded part of the bolt/setscrew, as shown in Fig. 1.

3. Use a pitch gauge to determine the pitch of the thread, as shown in Fig. 2.

4. Using a ruler, measure the length of the fastener from under the head, as shown in Fig. 3.

 

Corrosion protection 

A popular option to avoid corrosion is zinc plating, where a metal bond is formed between the steel and the zinc, which serves as a protective layer. 

Zinc-plated fasteners are ideally used in dry environments. Otherwise, stainless steel fasteners may be a better option. 

 

Colour 

The colour of the fastener is determined by a pigment additive during the electroplating process. That is why some fasteners appear to be gold (yellow-ish) or silver (clear) in colour. 

They do it just to enhance the appearance of the fastener. 

It does not have anything to do with durability.

gold silver bolts