Key Characteristics of Socket Head Bolts
Head Design:
Cylindrical Head: The head of the socket bolt is cylindrical with a smooth, rounded top,
providing a clean and low-profile appearance. This makes it suitable for applications where
minimal protrusion is needed.
Recessed Hex Socket: The defining feature is the hexagonal recess in the head, which allows for
tightening using a hex key or Allen wrench. This design provides excellent torque transfer,
allowing for higher clamping force than traditional fasteners.
Thread Type:
Socket head bolts typically come with Unified National Coarse (UNC) or Unified National Fine
(UNF) threads.
UNC threads are widely used for general-purpose fastening, while UNF threads are used in
applications requiring greater precision and stronger clamping forces.
Material:
Socket head bolts are available in various materials depending on the application’s
requirements:
Carbon Steel: Offers high tensile strength and is commonly used in heavy-duty applications.
Stainless Steel: Provides excellent corrosion resistance, suitable for outdoor or corrosive
environments.
Alloy Steel: Known for superior strength and heat resistance, making it ideal for high-stress or
high-temperature applications.
Titanium: Lightweight and strong, titanium socket head bolts are used in aerospace, automotive,
and medical applications due to their high strength-to-weight ratio and corrosion resistance.
Finish:
The surface finish on socket head bolts enhances durability and protects against corrosion:
Black Oxide: A common finish that provides mild corrosion resistance and a sleek, dark
appearance.
Zinc Plating: Provides corrosion resistance for general indoor use.
Galvanized: Offers superior protection against rust and corrosion, ideal for outdoor
applications.
PTFE Coating: Used for chemical resistance and low friction in specialized applications.
Types of Socket Head Bolts
Socket Head Cap Screws (SHCS):
Description: These bolts have a cylindrical head with a deep hex socket, allowing for a high
level of torque during installation.
Use Case: They are commonly used in machinery, equipment assembly, and precision applications
where strong fastening and a flush appearance are needed.
Applications: Industrial machinery, automotive engines, and aerospace components.
Flat Head Socket Cap Screws:
Description: These bolts feature a flat, countersunk head that sits flush with the surface when
fully tightened.
Use Case: Ideal for applications where a smooth, flat surface is required to avoid snagging or
interference with moving parts.
Applications: Aircraft assemblies, furniture, and precision instruments.
Button Head Socket Cap Screws:
Description: These bolts have a lower-profile, domed head with a shallow hex socket. They offer
a larger bearing surface but lower clamping force compared to cap screws.
Use Case: Used in applications where a smooth, rounded appearance is preferred, and heavy
clamping force is not necessary.
Applications: Electronics, lightweight structures, and consumer products.
Socket Set Screws (Grub Screws):
Description: These are headless screws with only a socket for installation. They are used to
secure one object inside another by applying pressure via the threaded shaft.
Use Case: Set screws are used in applications where space is limited or where the fastener needs
to be recessed.
Applications: Securing gears or pulleys to shafts, precision assemblies, and securing collars or
couplings.
Shoulder Bolts (Shoulder Screws):
Description: These bolts have a smooth, cylindrical shoulder between the head and the threaded
portion. The shoulder allows for rotation or sliding of parts around it.
Use Case: Used in applications that require precise alignment of parts or a pivot point.
Applications: Pivots, linkages, and machinery with moving parts.
Specifications of Socket Head Bolts
Thread Size:
Socket head bolts come in a range of thread sizes from #0-80 (smallest) up to 1-1/2 inches in
diameter for imperial sizes, and from M1.6 to M48 for metric sizes.
Length:
These bolts vary in length, with common lengths ranging from 1/4 inch to 6 inches for standard
bolts. In metric sizes, lengths can range from 5mm to 200mm or more.
Head Diameter:
The diameter of the socket head varies depending on the size of the bolt, but socket head bolts
generally have a smaller head diameter relative to their thread size, allowing them to fit in
tight spaces.
Tensile Strength:
Socket head bolts are designed for high-strength applications. Alloy steel socket cap screws can
have tensile strengths exceeding 180,000 psi (e.g., ASTM A574 standard), while stainless steel
versions typically offer tensile strengths of 70,000 to 100,000 psi.
Drive Size:
The size of the hex socket drive typically corresponds to the thread size of the bolt, with
common hex sizes ranging from 1/16 inch to 3/4 inch for imperial sizes, and 1.5mm to 19mm for
metric sizes.
Standards:
Socket head bolts must conform to certain standards to ensure their reliability and performance:
ASTM A574: Alloy steel socket head cap screws.
ISO 4762: Hexagon socket head cap screws.
DIN 912: European standard for hex socket cap screws.
Applications of Socket Head Bolts
Socket head bolts are used in heavy-duty machinery due to their high clamping force and flush
appearance. They are ideal for areas where space is limited and high torque is required.
Examples: Securing parts in CNC machines, manufacturing equipment, and industrial gearboxes.
The aerospace and automotive industries use socket head bolts due to their strength-to-weight
ratio and ability to fit in tight spaces. They are ideal for precision applications where
vibration resistance is critical.
Examples: Engine assemblies, transmissions, and aircraft fuselage components.
Due to their clean appearance and low-profile heads, socket head bolts are frequently used in
electronics and consumer goods where aesthetics and functionality are important.
Examples: Securing components in laptops, cameras, and home appliances.
Stainless steel socket head bolts are used in outdoor or corrosive environments where high
strength and corrosion resistance are required.
Examples: Bridge construction, architectural applications, and marine equipment.
In applications requiring precise alignment and strong clamping forces, such as optical or
medical instruments, socket head bolts provide a reliable fastening solution.
Examples: Mounting optics, securing medical devices, and assembling laboratory equipment.