ASTM F2437 / F2437M Technical Specification: Compressible-Washer-Type Direct Tension Indicators (DTI)
This specification defines stringent requirements for the manufacturing and operation of compressible-type Direct Tension Indicators (DTI) made from carbon and alloy steels. The products are designed for high-precision control of axial tension in fastening assemblies: anchors, studs, bolts, and screws. EV Group China supplies products that fully comply with these quality standards.
The standard covers a dimensional range for imperial products from 1.0 to 4.0 inches and metric sizes ranging from M6 to M72.
Classification and Technical Specifications of DTIs
The classification system for direct tension indicators is divided into two design types and four strength grades for imperial fasteners (5, 8, 55, 105), as well as two grades for metric products (8.8 and 10.9). The differences between the grades are based on compression load parameters at a calibrated gap.
| DTI Type | Strength Grade | Application Features |
|---|---|---|
| Type 1 | 5, 8 | Optimal for mounting on narrow bearing surfaces. |
| Type 2 | 55, 105 | Used for applications with increased bearing areas. |
Direct tension indicators are mounted under the bolt head or nut, ensuring contact with a hardened washer or a similar flat hardened surface. EV Group China recommends performing compatibility calculations for fasteners in accordance with the requirements specified for each specific DTI grade.
Important note: Imperial and metric measurement systems within this standard are independent. Combining parameters from different systems without engineering recalibration is not permitted and may lead to a breach of the fastening joint integrity.
Operation and Safety
The use of DTI indicators requires compliance with safety protocols when working with high-strength fasteners. The user is responsible for adhering to occupational health and safety regulations. This international standard was developed in accordance with WTO (TBT) principles, which ensures the unification of the quality of supplied products worldwide.