DTI Washers

DTI washers are used in structural steel construction where bolt tension is critical for the performance and safety of the connection. Common applications include:

• Bridges, buildings, and towers using high-strength bolting assemblies 
• Steel-to-steel connections in heavy construction or industrial frameworks 
• Retrofit or inspection-sensitive projects, where visible tension verification is required

By confirming bolt preload directly, DTI washers improve connection reliability, reduce the risk of under- or over-tightening, and ensure compliance with ASTM and AISC bolting standards.

DTI washers feature small, raised bumps (protrusions) on one face. During installation, these bumps are compressed as the bolt is tightened. When the correct tension is reached, the protrusions flatten within a specific compression load range, which corresponds to the minimum tension required for the associated bolt grade.

There are two ways to verify proper tension:

• Feeler gauge method – A feeler gauge is inserted between the flattened protrusions; when it no longer fits, correct tension is achieved. 
• Squirter™ DTI method – A colored silicone compound is released (“squirts”) from beneath the washer when the required compression load is reached, offering a fast, visual confirmation of proper tension.

Squirter™ DTI washers operate on the same principle as standard DTIs but incorporate a colored silicone indicator that extrudes visibly when correct tension is achieved. This innovation allows for instant visual confirmation in the field without the use of feeler gauges. Squirter™ DTIs simplify quality assurance and speed up inspection, making them especially valuable for large projects or limited-access installations.

DTI washers are manufactured to ASTM F959/F959M, the standard specification for load-indicating washers for structural steel joints. This specification defines mechanical performance, dimensional tolerances, and compression load ranges for washers compatible with A325 and A490 bolts (or their modern equivalents under ASTM F3125).

Load indicating washers for other bolt grades may fall under ASTM F2437, which covers tension-indicating washers for cap screws, anchors, and studs.

DTI washers are engineered for specific bolt grades because each bolt type requires a different compression load range to achieve proper tension.

• Type 325 DTIs correspond to A325 (or F3125 Grade A325) bolts. 
• Type 490 DTIs correspond to A490 (or F3125 Grade A490) bolts.

An A325 DTI cannot be used with an A490 bolt because its protrusions compress at a lower load range, causing incorrect tension readings. For example, a 1″ diameter A325 bolt requires compression between 51–61 kips, whereas an A490 bolt of the same size requires 64–77 kips. Using the wrong DTI washer type could result in under-tensioning and compromised connection strength.

Each DTI washer is designed to compress within a specific load range that corresponds to the required bolt tension. Under ASTM F959, Type 325 washers (for A325 bolts) and Type 490 washers (for A490 bolts) have different ranges to match their respective strength levels.

For instance, a ½-inch Type 325 washer compresses between 12 and 14 kips, while a Type 490 of the same size compresses from 15 to 18 kips. As sizes increase, these values rise proportionally—¾-inch washers compress between 28–34 kips for Type 325 and 35–42 kips for Type 490. At 1 inch, Type 325 washers range from 51–61 kips, compared to 64–77 kips for Type 490.

Because A490 bolts require higher tension, Type 490 washers are built to resist greater compression forces. Using the wrong washer type, such as a Type 325 with an A490 bolt, can cause premature compression and incorrect tension readings. Selecting the proper washer ensures accurate preload verification and compliance with ASTM F959 standards.

No. ASTM F959 explicitly prohibits using Type 325 washers with Type 490 bolts. Each washer type is calibrated for the unique tension characteristics of its bolt grade. Using an A325 DTI with an A490 bolt would result in the protrusions compressing too early, falsely indicating proper tension when the bolt has not yet achieved the required preload.

With the introduction of ASTM F3125, which consolidated A325 and A490 specifications, the same principle applies, you must select the DTI that matches the specific bolt grade being used under F3125.

Yes. ASTM F2437 defines additional load-indicating washers for cap screws, anchors, and studs across several grades:

• Type 1, Grade 55 – For use with ASTM F1554 Grade 55 or A307 bolts 
• Type 1, Grade 105 – For use with A193 B7 or F1554 Grade 105 bolts 
• Type 2, Grade 5 – For use with A449, A354 Grade BC, or J429 Grade 5 bolts 
• Type 2, Grade 8 – For use with A354 Grade BD or J429 Grade 8 bolts 

As with structural DTIs, each washer grade corresponds to a specific compression range and bolt strength level. Mixing mismatched grades will result in incorrect tensioning.

Portland Bolt stocks a complete range of DTI washers for A325 bolts, from ½″ through 1½″ diameters, manufactured domestically and supplied in plain or mechanically galvanized finishes. Additional sizes and configurations can be supplied upon request to meet specific project specifications.

DTI washers offer several key advantages in bolted joint assembly and inspection:

• Direct verification of bolt tension—eliminates reliance on torque or turn-of-nut methods. 
• Faster installation—protrusion compression or silicone extrusion provides immediate feedback. 
• Enhanced safety—ensures proper preload and prevents connection loosening or fatigue. 
• Reduced rework—inspectors can easily confirm proper tension visually or with a gauge.

This combination of accuracy and efficiency makes DTIs the preferred method for structural steel erection worldwide.