Frequently Asked Question

Short answer: No. Tension Control (TC) bolts are not manufactured in 1-3/8” or 1-1/2” diameters. Under the ASTM F3125 specification, TC bolts are produced up to a maximum diameter of 1-1/4”.

What is a Tension Control (TC) Bolt?

A Tension Control (TC) bolt, sometimes called a twist-off bolt, is a high-strength structural fastener designed for steel-to-steel connections in construction (e.g., buildings, bridges, and infrastructure projects).

Key characteristics:

• Preloaded installation: TC bolts are engineered to achieve a specific clamping force (tension) during installation.
• Spline (twist-off end): The bolt includes a splined end that shears off when the required tension is reached, providing a visual confirmation of proper installation.
• Fast installation: Installed using specialized shear wrenches, making them efficient for high-volume structural steel erection.
• Available as F1825 (A325) and F2280 (A490), and Grade 144.

These features make TC bolts a preferred choice when speed, consistency, and inspection reliability are critical.

What are the alternatives for larger diameters?

While TC bolts are not available above 1-1/4”, ASTM F3125 Grade A325, A490, and 144 heavy hex structural bolts are available in larger diameters, including:

• 1-3/8” diameter
• 1-1/2” diameter

At Portland Bolt, we manufacture these larger diameters regularly, including:

• A325, A490, and Grade 144 configurations
• Type 3 weathering steel (corrosion-resistant applications)

Although these bolts do not include a twist-off spline, they are fully compliant with structural specifications and are widely used in heavy structural connections.

How do you achieve proper tension without a TC bolt?

Standard A325, A490, and Grade 144 bolts can still be installed to the required tension using accepted methods:

• Direct Tension Indicator (DTI) washers
• Turn-of-nut method
• Calibrated wrench method

When paired with DTI washers, these assemblies provide a measurable and verifiable indication of bolt tension, similar in function to the inspection capability of TC bolts.

Are these larger diameters common?

Diameters like 3/4” and 1” are more typical in structural applications. However, 1-3/8” and 1-1/2” bolts are fully within the scope of ASTM F3125 and are used in applications requiring higher load capacity. These are less commonly stocked but routinely manufactured for project-specific requirements.

Summary

• TC bolts are limited to 1-1/4” maximum diameter under ASTM F3125
• Larger diameters (1-3/8” and 1-1/2”) are available as A325, A490, and Grade 144 heavy hex structural bolts
• Proper tensioning can still be achieved using DTIs or standard installation methods
• Portland Bolt manufactures these larger diameters, including weathering steel options

For project-specific requirements or quoting assistance, contact Portland Bolt to discuss your application.