Metric Bolts

What Are Metric Bolts?

Metric bolts are manufactured to meet international metric system standards. Metric fasteners are used in most manufacturing environments outside the United States. While imperial fasteners remain the standard in the US, metric fasteners are increasingly common in several domestic industries, including automotive and OEM applications.

Metric bolt strength is expressed as a property class, shown as two numbers separated by a decimal point. The first number represents one-tenth of the bolt's minimum tensile strength in MPa, and the second number represents the yield-to-tensile strength ratio as a percentage. For example, a Grade 8.8 bolt has a minimum tensile strength of 800 MPa and a yield strength of 80% of that value, or 640 MPa.

Types of Metric Bolts

Metric Hex Cap Screws (DIN 931 / DIN 933 / DIN 960 / DIN 961)

Metric hex cap screws feature a six-sided head that is driven by a wrench or socket. They are available in partial- and full-thread configurations and are used in virtually every industry. At RC Fasteners, we stock metric hex cap screws in steel grades 8.8 and 10.9, and stainless steel grades A2 and A4.

Metric Hex Flange Screws (DIN 6921)

Metric flange screws are hex cap screws with an integrated flange beneath the head. The flange spreads the fastening load over a larger surface area, which eliminates the need for a separate washer. Available in grade 10.9 with zinc-yellow CR+6 finish.

Metric Carriage Bolts (DIN 603)

Metric carriage bolts feature a round head and a square neck. The square neck resists rotation when installed. Metric carriage bolts are often used in wood-to-metal connections. Our stock includes grade 4.6 metric carriage bolts with zinc CR+3 finish.

Metric Bolt Grades and Materials

Grade 8.8 Bolts

Grade 8.8 bolts are a reliable all-purpose option for moderate to high-load jobs. They are the most common metric bolt grade, and are used across general industrial, mechanical, and structural applications. Grade 8.8 metric bolts are comparable to SAE Grade 5 in imperial sizing.

Grade 10.9 Bolts

Grade 10.9 bolts are significantly stronger than Grade 8.8 bolts, featuring a minimum tensile strength of 1,040 MPa and a yield strength of 940 MPa. They are used in high-load applications like automotive powertrain components, heavy industrial and manufacturing equipment, and structural applications.

Stainless Steel A2 (304) Bolts

A2 stainless steel bolts feature good corrosion resistance for outdoor and general-purpose use. They are common for applications that require exposure to moisture or mild chemicals (not recommended for saltwater marine or chloride-heavy environments).

Stainless Steel A4 (316) Bolts

A4 stainless steel bolts have significantly better corrosion resistance than A2, particularly in applications that require exposure to chlorides. Used for marine hardware, coastal installations, food processing equipment, and chemical processing applications.

Partial Thread vs. Full Thread: DIN 931 and DIN 933 Metric Bolts

• DIN 931 (Partial Thread): DIN 931 metric bolts are partially-threaded bolts. The shaft has an unthreaded section between the head and the threaded portion. That grip area bears shear loads directly, and the longer clamping length helps maintain bolt tension across thicker joint stacks. Partial thread bolts are used when fastening through two or more components with a nut on the back side.
• DIN 933 (Full Thread): DIN 933 metric bolts are fully threaded from tip to head. Full thread bolts maximize thread engagement and are used when threading into a tapped hole.

DIN 960 and DIN 961 follow the same partial and full thread approach as DIN 931 and DIN 933, but with a fine pitch thread rather than a standard coarse pitch thread.

Common Applications for Metric Bolts

Metric bolts are used across every major industrial sector. Because they are available in a wide range of materials, sizes, lengths, and finishes, they are extremely versatile and reliable. A few of the most common uses for metric bolts include:

• Automotive parts, including engine and suspension components
• Heavy-duty industrial machinery
• Manufacturing and material handling equipment, including conveyors and automation equipment
• Electronics hardware and components
• Structural components in construction applications
• Agricultural equipment, like tractors and machinery used in commercial farming

Order Metric Bolts from RC Fasteners

We maintain an extensive on-hand inventory of metric hex cap screws, metric carriage bolts, and hex flange screws across grades and finishes. Whether you need a one-time order or a long-term supply solution, we can get you the right metric bolts for your job fast. Contact us to learn more, or request a quote to get started on an order.