Scope
This specification covers the requirements for compressible-washer-type direct tension indicators capable of indicating the achievement of a specified minimum bolt tension in a structural bolt. Direct tension indicators are intended for installation under either a bolt head or a hardened washer. This specification provides for furnishing Types 325–3 and 490–3 to a Chemical Composition Requirement or a Corrosion Resistance Index (CRI) at the suppliers option. When “zinc coated” is specified, the direct tension indicators shall be zinc coated by the mechanical deposition process in accordance with the requirements of Class 55 of Specification B695. The direct tension indicators shall conform to the dimensional and related requirements of ASME B18.2.6.
Table 1: Chemical Composition Requirements
| Element | Composition % Heat Analysis | Composition % Product Analysis |
| Type 325/490 | Type 325-3/490-3 | Type 325/490 | Type 325-3/490-3 |
| Carbon | 0.30-0.55 | - | 0.27-0.58 | - |
| Manganese | 0.50-0.90 | - | 0.47-0.93 | - |
| Phosphorus, Max | 0.04 | 0.04 | 0.048 | 0.045 |
| Sulfur, Max | 0.045 | 0.05 | 0.053 | 0.055 |
| Silicon | 0.15-0.35 | 0.15-0.35 | 0.13-0.37 | 0.13-0.37 |
| Chromium | - | 0.45-0.65 | - | 0.42-0.68 |
| Nickel | - | 0.25-0.45 | - | 0.22-0.48 |
| Copper | - | 0.25-0.45 | - | 0.22-0.48 |
| Source: ASTM F959-09 |
Table 2: Direct Tension Indicator Gap for Compression Load Testing
| DTI Finish | Gap Inches - A325 | Gap Inches - A490 |
| Plain Finish | 0.015 | 0.015 |
| Mechanically Galvanized | 0.015 | - |
| Baked Epoxy Coating on Mech Galv Zinc | 0.015 | - |
| Source: ASTM F959-09 |
Table 3: Acceptable Range of Compression Loads (kips)
| DTI Size | Compression Load Range for 325/325-3 | Compression Load Range for 490/490-3 |
| 1/2" | 12-14 | 15-18 |
| 5/8" | 19-23 | 24-29 |
| 3/4" | 28-34 | 35-42 |
| 7/8" | 39-47 | 49-59 |
| 1" | 51-61 | 64-77 |
| 1-1/8" | 56-67 | 80-96 |
| 1-1/4" | 71-85 | 102-122 |
| 1-3/8" | 85-102 | 121-145 |
| 1-1/2" | 103-124 | 148-178 |
| Source: ASTM F959-09 |