Socket head cap screws or socket caps, have become the standard among high-strength fasteners needed to withstand the faster speeds and higher pressure of today’s machines, instruments and assemblies.
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Also known as their trademarked name, “Allen” screws, these fasteners are broadly used across various applications in many industries, including: aerospace, electrical motors, hydraulic equipment, instrumentation, tooling and fixtures, machinery, military and many more. Common uses include machine parts, die fixtures and assemblies.
1. What is a Socket Head Cap Screw?
Socket caps are externally threaded cap screws with a cylindrical head with a flat chamfered top and a hexagonal recess for internal wrenching. Hence, socket caps need less space than alternative fasteners.
Whereas nearly 90% of all commercial and industrial fasteners have a 2A fit, which offers a combination of performance, economy, and convenience, socket products generally have a 3A thread fit. 3A threads have restrictive tolerances often used where safety is a critical design consideration.
Because of their efficient design and thread fit, socket cap screws are ideal for precision assembly work with close tolerances and applications that need a well-tooled appearance.
2. What sizes are available?
Commercial socket caps, which conform to ASME B18.3, are available off the shelf in inch sizes starting as small as 0-80 diameter and are commonly available to diameter 1-1/2-6. Metric socket caps, which conform to DIN 912, are available from M1.4 – M48 diameter and are most common in coarse thread. Screw lengths and thread lengths are related to the diameter of the screws and all lengths may not be available in all materials and styles.
3. What materials and platings are available?
“Steel” socket caps off the shelf are alloy steel black oxide through heat treatment and are generally oiled. Stainless steel grades 18-8/303, A2, 316 and A4 are also commonly available. Other exotic materials such as brass, 416, A286 or special finishes may be available for special order with a lead time.
If you need an alloy steel fastener, but require greater corrosion resistance or a different look than black, consider stainless steel or zinc plating.
4. Are there special considerations when plating socket head cap screws?
We are so glad that you asked! If you are considering zinc plated socket caps, proceed with caution! Because of their tight tolerances and 3A fit, zinc plating a socket cap will often change the thread fit to a commercial nut fit. If you need a 3A fit, you must specify that on your purchase order so the factory can meet your thread fit needs when creating and plating your screws.
5. Other than size, material and plating, what other options are available?
The other main considerations when selecting socket caps are the head style and the drive type.
There are four main available head styles, and each serves a slightly different purpose.
Most socket caps come with a standard hexagonal socket drive. Other options include security pin-in-hex, pin-in-torx, or six-lobe torx versions in certain sizes and materials.
6. Are there other factors to consider?
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We’ve covered the most common variables including head style, diameter and thread, length, material and plating or finish. Here are a few of the other considerations you might be faced with based on the project and the bill of materials:
7. What level of certification is required?
Generally, a Certificate of Conformance or a COC is sufficient for your customer. Full certification with material certs, DFARS certification and test reports are often available for USA-made and mil-spec parts for a fee.
MF Supply is a leading supplier of Socket Head Cap Screws in alloy and stainless steel, including the brands Holo-krome and Blue Devil. We offer functional equivalents to the most popular national brands such as Fastenal, McMaster-Carr, MSC Industrial and Grainger.
Here at MF Supply, we offer:
For more detailed information about socket head cap screws, visit our website. And if you don’t see it listed, as always, ask us. “Finding the right screw for you” is our tag line after all!
For more than 40 years, MF Supply has helped American manufacturers streamline operations, saving them time and money with our sourcing expertise and unique supply chain strategies. We are a WBE/WOSB certified stocking distributor of fasteners and electronic components.
We work with the best-established factories in the United States and DFARS-certified countries, and stock a huge inventory including all major brands and equivalents. MF Supply provides solutions including: same-day drop ship direct from the factory; custom sizes, materials and plating options; and DFARS parts with full paperwork and Certificates of Conformance.
We creatively solve common problems including hard-to-find parts and long lead times. Our sourcing and reworking expertise includes fast turnaround for modification of existing parts, hard to find standards and specials, special threads, non-standard diameters and lengths, exotic materials, special platings and short runs. We provide functional equivalents to expensive brand name fasteners and help our customers save money while reducing lead times.
Hex bolts can be used either in pre-tapped holes or with nuts, depending on the application. They can then be tightened using a range of tools including a hex bolt wrench, socket sets, spanners, hex keys, and ratchet spanners.
The hexagon-shaped head ensures that it is easy to grip hex bolts from multiple angles, using different types of tool. This makes their installation and removal a straightforward process, plus ensuring it is also easy to loosen or tighten hex bolts once they are in situ.
The thread of a hex head bolt, also known as the screw thread, is the helical structure which comprises the main body of the bolt. It uses rotational force to drive the bolt firmly and securely into place, helping to provide easier entrance and exit into the material whilst also providing added grip. Both fully-threaded and partially-threaded hex bolts are available.
Partially-threaded hex bolts are only threaded from partway down the bolt’s length to the end. An unthreaded shank (also known as grip length) joins the threaded shank and the head. Partially-threaded bolts provide strong levels of resistance. Strain on the unthreaded part of the shank is prevented by the design which ensures that section has no weak spots.
Fully-threaded hex bolts are threaded from the end of the bolt right up to the head. They are ideal for use in heavy-duty fastening applications and are best suited to installation in pre-threaded holes. Properly installed fully-threaded hex bolts are designed to spread the pressure across the full length of the bolt, providing a greater level of strength than partially-threaded alternatives.
Hex bolts are typically manufactured from steel or stainless steel. While some manufacturers offer hexagonal bolts made from other materials, steel and stainless steel hex bolts are the norm.
Additionally, different coatings and finishes are available. These provide various qualities and appearances in order to suit a wide range of applications.
Popular hex bolt finishes include:
You may also find hex bolts made from other materials like brass, but this is less common. Although brass provides a high level of resistance against corrosion, it is usually more expensive so is often overlooked in favour of steel.
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