The Ultimate Guide To Low Head Shoulder Screws

Low head shoulder screws, also known as shoulder bolts, are used to allow the rotation of pulleys, linkages, and other moving parts in engines and mechanical applications. They feature a plain, non-threaded section under their heads to allow for free rotation, while their ends are threaded to secure them in place. Low head shoulder screws are used in applications where standard head height shoulder screws would not fit due to limited space. They are approximately half the height of standard cylindrical heads. Low head shoulder screws are available in various materials, including stainless steel, alloy steel, and brass, each with its own unique properties and applications.

Low-head shoulder screw dimensions

Low-head shoulder screws are used for fixture mounting applications. They are available in a variety of materials, including stainless steel and alloy steel, and can be purchased with different thread sizes and strengths.

The dimensions of low-head shoulder screws vary depending on the specific product and the manufacturer. Here are some examples of low-head shoulder screw dimensions:

• MISUMI: Part numbers FMSB4 to FMSB10, FMSBG4 to FMSBG10, and FSMSB4 to FSMSBH10. The thread size ranges from 10-40 to 10-60, with a 0.1 mm unit. The strength class for steel is 9.8 equivalent, and for stainless steel, it is A2-50. The thread part length F and shaft diameter tolerance are configurable by the user.
• Apex Fasteners: Standard-inch smooth head shoulder screws have a shoulder diameter tolerance of +0 to -0.001 inches and a shoulder length tolerance of +0.002 to 0 inches. The screws have a Class 2A thread fit. Standard-metric smooth head shoulder screws have a shoulder length tolerance of +0.05 mm to 0 mm and a Class 6g thread fit.
• Wixroyd: Ultra-low-head shoulder screws with a head height of approximately 1/3 that of normal shoulder screws. The product number is 36650, and the material is 303 stainless steel.
• Amazon: SCS250-LP series of low-profile shoulder screws with a shoulder diameter of 1/8", a head diameter of 0.2500", and a head height of 0.0940". The thread is #4-40, and the material is 303 stainless steel.

It is important to refer to the specific product specifications provided by the manufacturer to ensure the correct dimensions and compatibility for your application.

Low-head shoulder screw applications

Low-head shoulder screws are used for fixture mounting applications. They are available in various materials, including stainless steel and alloy steel, and are suitable for a range of applications.

The 303 series stainless steel low-head shoulder screws are suitable for pharmaceutical applications. The stainless steel used in these screws is also suitable for marine applications.

Low-head shoulder screws made from 304 stainless steel are also available.

Low-head shoulder screws made from alloy steel are another option and are suitable for standard applications.

Low-head shoulder screw materials

Low-head shoulder screws are available in a variety of materials, each with its own unique properties and applications. Here is an overview of some common materials used for low-head shoulder screws:

Stainless Steel

Stainless steel is a popular choice for low-head shoulder screws due to its corrosion resistance and strength. It is often used in applications where durability and resistance to the elements are important. There are different grades of stainless steel used, such as 303, 304, 316, and 416. Each grade has slightly different properties and is suitable for specific applications. For example, 303 stainless steel is suitable for pharmaceutical applications, while 316 stainless steel is often used in marine environments.

Alloy Steel

Alloy steel is another material option for low-head shoulder screws. Alloy steel is known for its strength and durability, making it suitable for applications where high strength and load-bearing capacity are required. The specific alloy used can vary, but 4137 alloy steel is commonly mentioned in relation to low-head shoulder screws.

Marine Stainless Steel (A4)

Marine stainless steel, also known as A4 stainless steel, is a specific type of stainless steel that is commonly used in marine applications. It has excellent corrosion resistance, making it suitable for use in saltwater environments. Marine-grade stainless steel is often used for low-head shoulder screws in boats, maritime equipment, and other applications where resistance to saltwater is crucial.

Other Materials

While stainless steel and alloy steel are the most commonly mentioned materials for low-head shoulder screws, other materials may be available from specialty manufacturers. These can include exotic alloys, plastics, or other materials tailored to specific applications.

In summary, the choice of material for low-head shoulder screws depends on the specific application and environmental conditions. Stainless steel, alloy steel, and marine-grade stainless steel are the most common choices, each offering unique properties such as corrosion resistance, strength, and durability.

Low-head shoulder screw finishes

Low-head shoulder screws are available in a variety of materials and finishes. The most common materials include stainless steel and titanium.

Stainless Steel Shoulder Screws

There are three grades of stainless steel shoulder screws:

• A2 series: standard-grade stainless steel with good strength and corrosion resistance, but not suitable for very harsh environments like saltwater.
• 416 series: made from harder stainless steel with improved shear strength, but more prone to corrosion.
• A4 series: very resistant to corrosion but considerably more expensive than other stainless steel options.

Titanium Shoulder Screws

Titanium shoulder screws are also available and provide excellent strength-to-weight ratio and corrosion resistance.

Finishing Options

Finishing options for shoulder screws include:

• Black oxide coating: provides a black finish and improves corrosion resistance.
• Zinc plating: provides an anti-corrosion layer over steel.
• Passivation: a process to remove impurities and improve corrosion resistance.
• Ultrasonic cleaning: used for ultra-clean applications.

Low-head shoulder screw drives

Low-head shoulder screws are typically used for food and pharmaceutical applications but are not suitable for marine environments. They are used as fasteners joining two pieces of an assembly where maintaining alignment is critical.

Low-head shoulder screws have an unthreaded shoulder made with an undersized tolerance to fit bearings, linear motion bushings, and other precision components. They are often used in imaging equipment, surgical tools, measuring devices, laboratory instruments, enclosures, and optical fixtures.

The shallow head of low-head shoulder screws makes them the right size to hold components in tight spaces. They are typically two-thirds the head height of standard head height shoulder screws, although ultra-low-profile versions are also available, with a head height of approximately one-third that of normal shoulder screws.

Low-head shoulder screws are available with a variety of drives, including hex socket, slotted, and 6-lobe.

Frequently asked questions