Product Introduction
Tension control bolt assemblies manufactured to ASTM F1852, the standard covering twist-off type high-strength structural fasteners for steel-to-steel connections. The fastener includes a heavy hex head, a spline end that shears at a calibrated preload, and a matching nut and washer. Spline break-off provides visual confirmation that the required bolt tension has been reached, eliminating field torque measurement. Inch diameters from 1/2″ to 1‑1/2″ are standard, with larger sizes available on request.

Material & Mechanical Properties
Produced from heat-treated medium carbon alloy steel in accordance with ASTM F1852 chemistry and mechanical requirements. Two strength levels are supplied: Type 1 equivalent to ASTM A325 with a minimum tensile strength of 120 ksi (830 MPa), and Type 2 equivalent to ASTM A490 with a minimum tensile strength of 150 ksi (1040 MPa). Charpy V‑notch values, proof load, and tensile properties are certified per heat lot with full traceability.

Spline & Installation
The bolt carries a heavy hexagon head at one end and a spline extension at the threaded tip. A calibrated shear wrench engages the nut and spline simultaneously; the spline fractures when the design tension is achieved. The absence of the spline serves as direct visual verification that correct preload has been applied, eliminating the risk of thread stripping, galling, or under‑torque that can occur with torque‑only methods.

Surface Protection
The standard finish is black oxide, supplying a uniform dark appearance and moderate corrosion resistance for indoor and sheltered applications. For outdoor structural applications, hot‑dip galvanizing to ASTM A153 Class C is specified, with nuts overtapped to accommodate the coating allowance. Other protective coatings are available subject to project requirements and hydrogen embrittlement control protocols for high‑strength bolting.

Application Suitability
Steel‑frame buildings, bridges, highway structures, dock facilities, and heavy industrial construction where ASTM F1852 bolting is called out on the erection drawings. Also used as headed anchor bolts in concrete foundations when high‑strength fasteners with built‑in tension indication are specified. Suitable for slip‑critical, bearing, and direct‑tension joints in both new construction and structural retrofits.