What size is a header bolt?

Header bolts, also known as carriage bolts, are a type of fastener commonly used in construction, woodworking, and various other applications. The size of a header bolt refers to its diameter and length, which are crucial factors in determining its strength and suitability for a particular project.

What is the Standard Size of a Header Bolt?

The standard size of a header bolt is typically measured in inches or millimeters. The most common sizes range from 1/4 inch (6.35 mm) to 1 inch (25.4 mm) in diameter, with lengths varying from 1 inch (25.4 mm) to 6 inches (152.4 mm) or more. The specific size required will depend on the application and the materials being fastened together.

Factors to Consider When Choosing Header Bolt Size

• Diameter: The diameter of the header bolt determines its strength and the size of the hole required in the materials being fastened. Larger diameters are generally stronger but may require larger holes, which can weaken the material.


• Length: The length of the header bolt must be long enough to pass through the materials being fastened and allow for the nut and washer to be properly secured. However, the bolt should not be too long, as this can lead to interference or damage.


• Material Thickness: The thickness of the materials being fastened together will influence the required bolt length. Thicker materials will require longer bolts.


• Load-Bearing Capacity: The expected load or stress on the fastener should be considered when selecting the bolt size. Heavier loads will require larger, stronger bolts.

By carefully considering these factors, you can ensure that you select the appropriate header bolt size for your specific application.

What size is the header bolt on a Ford 302?

The standard header bolt size for a Ford 302 is 3/8"-16 with a length of 3/4" to 1". The bolt head is typically a 3/8" hex, but other styles like 12-point or Allen head are also available, and some specialized bolts can be longer or have a different thread size. 
Bolt size breakdown

• Thread Size: 3/8"-16 UNC 
• Length: Common lengths are 3/4" or 1" 
• Head Style: Most commonly a hex head, but other options like 12-point or Allen head are available 
• Other common variations: Some kits offer slightly longer bolts or studs as an alternative. 

How to choose the right bolts

• Standard application: For most applications, 3/8"-16 x 3/4" or 1" bolts are appropriate. 
• Consider the head style: If you have limited space, consider a bolt with a smaller head size or a 12-point style for better access. 
• Look for locking features: For high-vibration applications, consider locking header bolts to prevent them from coming loose. 

What size bolts are exhaust bolts?

Exhaust bolt sizes vary widely depending on the vehicle, with common sizes including metric options like M8 x 1.25 and M10 x 1.5, as well as imperial sizes like 3/8 inch x 1 1/4 inch. Always confirm the specific size needed for your vehicle's application, such as the exhaust manifold or flange, as it can differ based on the make, model, and component.
 
Common exhaust bolt sizes

• Metric:
  • M8 x 1.25: A common size for many modern LS/LT engines, with a typical length of 25mm. 
  • M10 x 1.5: Frequently used for exhaust manifolds and flanges. 
  • M10 x 1.25: Another metric option, sometimes used for exhaust manifold bolts. 
• Imperial:
  • 3/8 inch: A common imperial size for some engines, such as the Ford 351W, which may use 3/8 x 1 1/4 inch bolts. 
  • 7/16 - 14: This size refers to the thread diameter and pitch, often found in older or specific applications like some classic Dodge/Chrysler models. 

How to find the correct size

• Identify the location: Determine if you need a bolt for the exhaust manifold, flange, or a clamp. 
• Check the vehicle's service manual: The most accurate information for your specific vehicle can be found in the repair or service manual. 
• Measure the old bolt: If possible, take a measurement of the old bolt to find its diameter, thread pitch, and length. 
• Look up your vehicle's specific parts: Search online for "exhaust bolt size for [your vehicle's year, make, and model]" or "[component] exhaust bolt size". 

How to tell what size a bolt head is?

To measure a bolt head size, first determine the bolt's diameter by measuring across the threads with a ruler or calipers, then use a bolt gauge or chart to find the corresponding head size. Bolt head sizes are often related to the diameter, with a 1/2 inch bolt typically requiring a 7/8 inch wrench, and metric sizes like M6 or M8 also correspond to a specific head size. 
This video demonstrates how to measure a bolt's diameter using a bolt gauge: 56sBoltsandNuts comYouTube · Feb 28, 2024
How to measure the head size

1. Measure the bolt diameter: Use calipers or a ruler to measure the distance across the widest part of the bolt's threads. 
2. Use a bolt gauge: A bolt gauge has holes labeled with diameters. Insert the bolt into the smallest hole it fits snugly into to find its diameter. 
3. Use a chart: Cross-reference your measured diameter with a chart that lists standard and metric bolt head sizes to find the corresponding head size. 
4. Consider the type of bolt: For some special bolts, like countersunk bolts, the head size is measured differently. In these cases, the head is not measured, but instead, the head is measured from the top to the bottom of the threads. 

Things to consider

• Standard vs. metric: Standard bolts are measured in inches and metric bolts in millimeters. 
• Head markings: Some bolts have markings on their heads that can help identify their size. 
• Tools: A ruler, tape measure, or calipers are helpful for measuring bolts. 

This video explains how to determine the correct size and fit of a bolt: 47sBoltsandNuts comYouTube · Oct 9, 2020

What size are header collector bolts?

Common header collector bolt sizes are 3/8"-16 and M10 x 1.5, with lengths like 1" to 2-1/4" being frequent choices. The specific size can vary based on the vehicle and collector flange design, so it's best to check your application's specifications or consult the exhaust system manufacturer for the correct size. 
Common bolt sizes

• Metric: M8 x 1.25, M10 x 1.5
• SAE (Imperial): 5/16"-18, 3/8"-16 

Common bolt lengths 

• Metric: 22mm, 30mm
• SAE (Imperial): 3/4", 1", 1-1/4", 2-1/4" 

Factors to consider

• Flange type: Some flanges may require different bolt sizes. For example, some 2-bolt flanges use M10 bolts, while others use M8 or 3/8"-16 bolts. 
• Vehicle application: The manufacturer of your vehicle or exhaust system will have the correct specifications for your application. 
• Bolt type: You can choose from various styles, such as standard hex bolts, hex-head bolts, or locking bolts designed to prevent vibration and leaks.