A cap screw is a type of fastener used to make mechanical connections. They come in a variety of sizes and materials to match the needs of specific applications, such as metal fabrication or automotive manufacturing.
They differ from hex bolts in many ways, including how they are installed. In this article, we will explore the differences between these two types of fasteners to help you choose the right one for your project.
Material
Hex cap screws are made from a variety of metals to suit varying applications and environments. Alloy steel, for instance, resists corrosion and offers a high level of strength. Chromium-molybdenum alloys and high-strength nickel-chromium alloys are used for harsh environments, as they withstand oxidation and elevated temperatures.
Hex head cap screws are a general-purpose threaded fastener designed for insertion in pretapped holes or to use alongside nuts. These screws stretch when tightened, creating a tensile load that clamps parts together.
They are suitable for use in a wide range of applications including machine tools and hydraulic braking systems, as well as home furniture and electrical projects. They’re also a critical component in power plants and aerospace industries, where precision and reliability are essential. They adhere to ISO and ASTM standards for durability and strength. Specialty materials like abrasion-resistant stainless steel provide exceptional resistance to wear and tear. They can be cold formed and forged, then heat treated for hardening and toughness.
Threads
Unlike a bolt, cap screws do not use a nut to install and tighten. They are threaded into tapped holes or hex-shaped cavities (socket head caps) and can be made in a variety of lengths.
Their threads are usually rolled, which provides smoother and more uniformly formed threads than cut ones. Coarse threads are recommended for general use and work well with lower strength materials, while finer threads offer greater strength in the same diameter.
In terms of thread size, a screw’s major diameter and pitch are the key parameters to consider. The latter refers to the distance between each thread crest (also known as the included angle), and it can range from one start to up to four starts. The number of starts determines whether a screw has coarse or fine threads. Fine threads require less torque to tighten and loosen than coarse threads, so they are a good choice for most applications. Ideally, no more than two or three threads should show beyond the nut height, which can be measured using go/no-go gauges and optical comparators.
Head
Cap screws are used to create a mechanical connection that resists loosening over time. They’re directly tightened into a threaded or tapped hole and do not require a nut. They can be applied to heavy duty projects that need a fastener that can handle high amounts of clamping force.
Socket head capscrews have a built-in hexagonal socket in the center for turning with an Allen wrench or hex key. They have a low-profile design and are ideal for applications with limited space for the screw. They also provide high shear strength, ensuring that they can hold together even under substantial pressure.
These fasteners are made from a variety of materials to meet the specific needs of each application. They’re available in stainless steel and other specialty alloys to withstand different environmental and strength requirements. They’re used in industries such as automotive, aerospace, and energy to ensure that the products they produce can withstand rigorous demands.
Length
The length of a cap screw depends on the amount of force it is expected to generate in its mechanical connection. A high amount of clamping force can put a lot of strain on the screw and cause it to loosen over time. The length of a cap screw is measured from below the head to the last complete thread.
A cap screw can be used in a variety of environments and applications, but it is important to understand the forces that will be exerted on the fastener. This information will help you determine which material and threading pattern is best for your application.
A socket head cap screw features a cylindrical head with a hexagonal socket (also known as an Allen socket) in the center. This type of screw requires a hex key to install. It is commonly used in applications that require a low-profile design or access to tight spaces. These screws are available in a wide range of materials to meet various environmental and strength requirements.