The designation "1/4-20" refers to a specific type of bolt, indicating its diameter and threads per inch. Understanding these dimensions is crucial for selecting the right fastener for your project, ensuring a secure and reliable connection. This guide will break down the meaning of these numbers and provide further information about related specifications.
What Does 1/4-20 Mean?
The "1/4" in "1/4-20" signifies the nominal diameter of the bolt's shank (the unthreaded portion). This means the bolt is approximately 1/4 of an inch (6.35 mm) in diameter. It's important to note that this is a nominal measurement; the actual diameter might slightly vary due to manufacturing tolerances.
The "20" indicates the number of threads per inch (TPI). This specifies the density of the threads along the bolt's length. A higher TPI means finer threads, while a lower TPI indicates coarser threads. 20 TPI is a relatively common thread pitch, offering a good balance between strength and ease of assembly.
What are the other important dimensions of a 1/4-20 bolt?
Besides the diameter and threads per inch, several other dimensions define a 1/4-20 bolt:
Head Style and Dimensions:
The bolt head style varies widely; common styles include:
- Hex Head: The most common type, featuring a hexagonal shape for wrench engagement. Dimensions include the head's width across flats and its height.
- Pan Head: A low-profile head with a slightly rounded top.
- Button Head: A very low-profile head, typically used where a flush surface is required.
- Flat Head: A head that sits flush or nearly flush with the surface when tightened.
- Oval Head: Similar to pan head but with a more elongated oval shape.
Each head style will have its own specific dimensions, impacting overall bolt length and the required wrench size. You'll need to specify the head style when ordering.
Bolt Length:
The length of a 1/4-20 bolt is measured from the underside of the head to the end of the shank. This is crucial for determining how far the bolt will extend through the materials being fastened. Bolt lengths are typically specified in inches or millimeters.
Thread Length:
This refers to the portion of the bolt that is threaded. This dimension is often shorter than the overall bolt length to allow for some unthreaded shank to provide a better grip and distribution of clamping force.
Tolerance:
Manufacturing tolerances account for slight variations in dimensions. These are usually specified in industry standards like ASME B1.1. It's important to check the tolerance for your specific application.
What materials are 1/4-20 bolts made from?
1/4-20 bolts can be manufactured from a variety of materials, each offering different strength, corrosion resistance, and other properties:
- Steel: A common and cost-effective choice, often offering good strength. Variations include stainless steel (for corrosion resistance) and other alloyed steels for enhanced properties.
- Stainless Steel: Highly resistant to corrosion, ideal for outdoor or wet environments. Different grades of stainless steel (e.g., 304, 316) offer varying corrosion resistance.
- Brass: Offers good corrosion resistance and is often used in applications where electrical conductivity is a consideration.
- Aluminum: Lightweight and often used where weight is a concern.
Where can I find the exact dimensions for a specific 1/4-20 bolt?
The exact dimensions of a 1/4-20 bolt will depend on the specific manufacturer, head style, and material. Consult the manufacturer's specifications or a comprehensive fastener catalog for detailed dimensional information. You can typically find these details online or in engineering handbooks.
This information should give you a solid understanding of 1/4-20 bolt dimensions and related factors. Remember to always consult the manufacturer's specifications to ensure you are using the correct fastener for your particular application.
