Tension Control Bolts
Tension control bolts (TC bolt) is a specialized type of structural bolt used in steel frame construction and other high-strength fastening applications. TC bolts are typically a pre-assembled set of a bolt, nut, and washer. They have a rounded or domed head and a partially threaded shank. The primary purpose of TC bolts is to ensure consistent and accurate tensioning in structural steel connections. This precision is essential for ensuring the integrity and safety of structures, especially in critical applications like bridges and buildings. By eliminating the guesswork associated with traditional bolt tightening methods, TC bolts help prevent under-tightening or over-tightening, which can lead to connection failures.
ASTM F3125 Grade F1852/F2280 (A325/A490 equivalent)
Tension Control Structural Bolts are installed with an electric installation tool. The bolt is calibrated so the spline tip twists-off when the proper bolt tension is achieved, eliminating the need to rely on a calibrated wrench or an operator's skill to apply the proper tension. Visual inspection to confirm the spline has twisted off reduces the expense of more costly bolting inspections.
Assemblies must be protected from dirt and moisture at the job site, and lubrication must not be removed or changed from the as-delivered condition. An ASTM F436 flat washer must be placed under the nut in all cases. To determine bolt length, add additional length (from table on right) to grip length, and round up to nearest bolt length.
| Bolt Diameter (inches) | Additional Length |
| 5/8 | 7/8" |
| 3/4 | 1" |
| 7/8 | 1 1/8" |
| 1 | 1 1/4" |
| 1 1/8 | 1 1/2" |
- Reliable Tensioning: TC bolts, when used with a calibrated installation tool, guarantee precise and consistent tension, contributing to a secure and stable joint.
- Materials & Integrity: All TC bolts are made from steel, conforming to ASTM F3125, Grade A325 or A490 standards. They have a specialized coating that shouldn't be altered, as this affects their holding power and corrosion resistance.
- Factory-Designed Assembly: TC bolts are designed and manufactured to meet specific standards and should be used as a complete assembly, as-is from the manufacturer.
| Inch | Metric | Inch | Metric | |||||
| 120 ksi Min Tensile | 830 MPa Min Tensile | 150 ksi Min Tensile | 1040 MPa Min Tensile | |||||
| Type 1 | Type 3 | Type 1 | Type 3 | Type 1 | Type 3 | Type 1 | Type 3 | |
| Style - Twist-Off Bolts | ||||||||
| Dimensions, ASMEB | B18.2.6 | B18.2.6 | F | F | B18.2.6 | B18.2.6 | F | F |
| Thread Fit, ASMEB | B1.1 UNC 2A | B1.1 UNC 2A | F | F | B1.1 UNC 2A | B1.1 UNC 2A | F | F |
| Grade MarkingA,D | A325TC | A325TC | F | F | A490TC | A490TC | F | F |
| Alt. MarkingA,C | A325 | A325 | F | F | A490 | A490 | F | F |
| Recommended Nut and Washer | ||||||||
| Plain Nut | A563 DH | A563 DH3 | A563M 10S | A563M 10S3 | A563 DH | A563 DH3 | A563M 10S | A563M 10S3 |
| Suitable AlternativeE | DH3, D, C, C3 | C3 | 8S, 8S3, 10S3 | 8S3 | 10S3 | |||
| Coated Nut | A563 DH | A563 DH3 | A563M 10S | A563M 10S3 | A563 DH | A563 DH3 | A563M 10S | A563M 10S3 |
| Flat, Bevel or Thick Washer if used | F436 - 1 | F436 - 3 | F436M - 1 | F436M - 3 | F436 - 1 | F436 - 3 | F436M - 1 | F436M - 3 |
B Manufactured to the latest revision at the time of manufacture, UNC for inch series and Metric Coarse (MC) for Metric Series.
C Previously used markings may be sold and used indefinitely, bolts must be manufactured to current marking requirements upon initial publication of this standard.
D Other distinguishing markings for type 3 are permitted at the manufacturers option.
F Metric dimensions and requirements for this style have not been established.