Direct Tension Indicator (DTI) washers are essential components in structural steel connections, engineered to ensure proper bolt tensioning without relying on torque. By featuring specialized protrusions or "bumps" that compress as the bolt is tightened, DTI washers provide a visual and measurable indication of achieved tension. Approved by the Research Council on Structural Connections (RCSC), these washers are critical for guaranteeing the structural integrity of high-strength bolting assemblies in bridges, buildings, and industrial frameworks.
At FULLERKREG, we manufacture premium fastening solutions designed for critical applications. Explore our complete ASTM F959 DTI Squirtern Washer collection to find the exact specifications required for your next structural steel project.
ASTM F959 Specifications
| Property | Specification |
|---|---|
| Standard | ASTM F959 / F959M |
| Material | Medium carbon steel, quenched and tempered |
| Max Hardness | 37 HRC |
| Types | Type 325 (for A325/F1852), Type 490 (for A490/F2280) |
| Finish Options | Plain, Mechanically Galvanized, Hot-Dip Galvanized |
DTI Washer Dimensions Chart
| Bolt Diameter | Washer OD | Washer ID | Thickness | Bump Height | Applicable Bolt Grade |
|---|---|---|---|---|---|
| 1/2" | 1.188" | 0.531" | 0.122" | 0.045" | A325 / A490 |
| 5/8" | 1.500" | 0.656" | 0.122" | 0.045" | A325 / A490 |
| 3/4" | 1.750" | 0.812" | 0.136" | 0.045" | A325 / A490 |
| 7/8" | 2.000" | 0.937" | 0.136" | 0.045" | A325 / A490 |
| 1" | 2.250" | 1.062" | 0.136" | 0.045" | A325 / A490 |
| 1-1/8" | 2.500" | 1.187" | 0.136" | 0.045" | A325 / A490 |
| 1-1/4" | 2.750" | 1.312" | 0.136" | 0.045" | A325 / A490 |
| 1-1/2" | 3.250" | 1.562" | 0.136" | 0.045" | A325 / A490 |
Type 325 vs. Type 490 DTI Washers
ASTM F959 defines two main configurations of DTI washers based on their structural application. Type 325 DTI washers are explicitly calibrated to be used with ASTM A325 or F1852 structural bolts. Type 490 DTI washers are heat-treated to higher specifications to endure the greater tension requirements of ASTM A490 or F2280 bolts. It is vital to match the exact Type with the appropriate bolt grade to ensure the connection will perform properly under structural loads.
Squirtern DTI Washers
To further enhance the speed and reliability of bolting inspection, FULLERKREG offers advanced Squirtern DTI washers. These function exactly like standard DTI washers but feature a specially formulated silicone compound embedded in the protrusions. As the fastener is tightened and the bumps compress, the silicone extrudes out radially, giving an immediate visual indication of correct tension.
Benefits of Squirtern DTI washers include:
- Visual confirmation of required tension without inserting a feeler gauge into every bolt gap.
- Rapid and more accurate structural inspections.
- Improved safety by allowing installers and inspectors to verify connections from a safe distance.
- Reduced labor and installation time across the entire job site.
Upgrade your connections with our ASTM F959 Squirtern DTI washers.
Installation Methods
DTI washers can be installed in several RCSC-approved configurations:
- Method 1 (DTI under bolt head): The DTI is placed directly under the bolt head with protrusions facing the underside of the head. The nut is then turned to tighten.
- Method 2 (DTI under nut): The DTI is placed under the nut with protrusions facing the nut. A hardened flat washer must be inserted between the nut and the DTI to prevent rotational damage.
- Method 3 (DTI under head, head turned): A hardened flat washer is placed between the bolt head and the DTI bumps when the bolt head must be the element turned.
- Using Bevel Washers: When tightening on a sloped surface, bevel washers must be placed against the flange to provide a flat surface for the DTI, ensuring the bumps compress evenly.
Feeler Gauge Inspection
For standard F959 DTI washers, the RCSC specifies a clear four-step inspection process using a feeler gauge:
- Sample testing: Test a representative sample of assemblies in a tension calibrator to ensure the bolts meet minimum tension requirements.
- Determine test gap: Record the final gap between the DTI and the flat surface after achieving the target tension on the calibrator.
- Set job inspection gap: Establish the maximum gap allowed based on the test (often 0.015" for uncoated or 0.005" for coated washers).
- Field verification: Attempt to insert the job inspection feeler gauge into the gaps between the DTI protrusions on installed bolts. The gauge should be refused in at least half of the gaps.
Finish Options
| Finish Options | Standards | Use Case |
|---|---|---|
| Plain | - | General interior structural steel. |
| Mechanically Galvanized | ASTM B695 | Moderate outdoor corrosion resistance. |
| Hot-Dip Galvanized | ASTM A153 | Maximum long-term outdoor corrosion protection. |
Frequently Asked Questions
What is the ASTM standard for DTI washers?
The standard is ASTM F959, covering the requirements for compressible-washer-type direct tension indicators used in structural steel connections.
What sizes do DTI washers come in?
They are available in sizes matching standard structural bolts, typically from 1/2" up to 1-1/2".
How do I know if a DTI washer is Type 325 or Type 490?
DTI washers are clearly marked on the face with their respective grade designations, such as "325" or "490".
Can DTI washers be reused?
No, DTI washers are strictly for single-use applications. Their protrusions plastically deform during tightening.
What is the difference between standard DTI and Squirtern DTI washers?
While standard DTIs require a feeler gauge for tension verification, Squirtern DTIs feature a silicone compound that extrudes visually to indicate correct tension, saving time.
Where can I buy ASTM F959 DTI washers?
You can purchase them from FULLERKREG. Check out our ASTM F959 DTI Squirtern Washer collection or email us at sales@fullerkr.com.
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