In the field of structural steel bolting, achieving the correct bolt pretension is critical to the integrity of the connection. While standard Direct Tension Indicator (DTI) washers rely on a precise feeler gauge inspection to verify this pretension, advanced Squirtern DTIs offer a rapid visual confirmation through silicone extrusion. Regardless of the type used, understanding the fundamental ASTM F959 inspection protocols is essential for quality control. This guide outlines the standard procedures approved by the Research Council on Structural Connections (RCSC). For premium fastening solutions, explore the FULLERKREG DTI washer collection.
What Is a Feeler Gauge for DTI Washers?
A DTI washer feeler gauge is a precision-machined piece of hardened steel used to measure the gap between the washer's protrusions and the bearing surface. During the tightening process, the bumps on the DTI compress. The feeler gauge acts as a definitive go/no-go tool to ensure the gap has closed sufficiently, proving that the required tension has been applied to the bolt. This simple yet highly accurate tool eliminates the uncertainties associated with torque-based tightening methods.
Why Feeler Gauge Inspection Matters
- Objective Measurement: It provides a physical, non-disputable verification of bolt tension, independent of torque variables like lubrication or thread condition.
- Traceability: Precise gap measurements allow quality control teams to document connections accurately for project records.
- Compliance: It ensures the structural steel bolting meets strict RCSC and ASTM F959 requirements.
- Safety: Proper inspection guarantees that critical load-bearing joints will perform as engineered, preventing catastrophic failures.
Required Tools and Equipment
| Equipment | Purpose & Specification Details |
|---|---|
| Feeler Gauge | 0.015" for uncoated washers or 0.005" for coated washers. Used to measure the post-tension gap. |
| Skidmore-Wilhelm Calibrator | Hydraulic tension calibrator used during sample testing to measure actual bolt tension. |
| Torque Wrench / Nut Runner | Pneumatic, electric, or manual wrenches capable of tightening high-strength structural bolts. |
| Inspection Log Sheet | Standardized forms for recording test gaps, field refusals, and lot traceability data. |
Step-by-Step Inspection Procedure
The RCSC mandates a strict inspection protocol to ensure accurate DTI washer gap inspection:
- Step 1: Sample Testing. Test a minimum of 3 representative fastener assemblies in a tension calibrator. Tighten until the tension is at least 105% of the specified minimum pretension.
- Step 2: Determine Test Gap. Using the feeler gauge, count the number of acceptances and refusals in the gaps between the DTI protrusions of the sample assembly.
- Step 3: Establish Job Inspection Gap. Set the Job Inspection Gap criteria. The field installation must require MORE feeler gauge refusals than were observed during the sample test to ensure adequate tension.
- Step 4: Field Inspection. Using the identical feeler gauge from the sample test, verify installed bolts on the structure. Compare the field refusals to the established Job Inspection Gap to approve the connection.
Squirtern DTI Washer Inspection
FULLERKREG's innovative Squirtern DTIs significantly accelerate the inspection process. These washers feature a highly visible orange silicone extrusion that squirts out from the bumps when correct tension is achieved, offering immediate visual confirmation. While this visual cue drastically reduces the need for 100% feeler gauge field verification, RCSC standards still require the initial sample testing process to calibrate the visual extrusion against actual tension. Periodic feeler gauge verification during installation is also recommended to ensure ongoing accuracy. Upgrade your workflow with FULLERKREG Squirtern DTI washers. For technical data or orders, email sales@fullerkr.com.
Common Inspection Errors
| Error | Consequence | Prevention |
|---|---|---|
| Wrong gauge thickness | False acceptances or rejections of tension. | Verify 0.015" for uncoated, 0.005" for coated DTIs. |
| Skipping sample testing | No baseline for the Job Inspection Gap. | Mandate pre-installation Skidmore testing for all lots. |
| Inspecting before full tensioning | Incomplete joint consolidation. | Complete the snug-tightening phase before final tensioning. |
| Reusing DTIs | Inaccurate tension reading due to deformed bumps. | Strictly enforce single-use policy for all DTI washers. |
| Dirty/damaged gauges | Gauge sticks, leading to false refusal readings. | Clean gauges daily and replace if bent or scratched. |
| Incorrect Job Inspection Gap | Under-tensioned bolts passing inspection. | Ensure field refusals exceed sample test refusals. |
Feeler Gauge Thickness by Bolt Diameter
| Bolt Diameter | Typical Feeler Gauge Thickness | Min. Pretension (A325) kips | Min. Pretension (A490) kips |
|---|---|---|---|
| 1/2" | 0.015" (uncoated) / 0.005" (coated) | 12 | 15 |
| 5/8" | 0.015" (uncoated) / 0.005" (coated) | 19 | 24 |
| 3/4" | 0.015" (uncoated) / 0.005" (coated) | 28 | 35 |
| 7/8" | 0.015" (uncoated) / 0.005" (coated) | 39 | 49 |
| 1" | 0.015" (uncoated) / 0.005" (coated) | 51 | 64 |
| 1-1/8" | 0.015" (uncoated) / 0.005" (coated) | 56 | 80 |
| 1-1/4" | 0.015" (uncoated) / 0.005" (coated) | 71 | 102 |
| 1-1/2" | 0.015" (uncoated) / 0.005" (coated) | 103 | 148 |
Inspection Documentation Requirements
- Sample Test Report: Records the initial Skidmore testing data and tension results.
- Job Inspection Gap Record: Documents the established gap and refusal criteria for the specific lot.
- Field Inspection Log: Tracks the ongoing verification of installed assemblies across the structure.
- Material Certifications (MTRs): Traceability documents matching the DTI lots to the inspection records.
When to Use Squirtern DTIs
Squirtern DTIs are highly advantageous in specific project scenarios:
- High-volume bolting: Significantly reduces time spent checking every single bolt with a feeler gauge.
- Limited access areas: Visual extrusion can be seen without needing physical clearance for a feeler gauge.
- Weather exposure: Rapid visual checks minimize inspector time in harsh environmental conditions.
- Inspector shortage: Streamlines the QC process when third-party inspection resources are constrained.
- Accelerated schedules: Helps contractors meet aggressive deadlines by speeding up the connection approval phase.
Frequently Asked Questions
What is a DTI washer feeler gauge?
It is a precise metal tool used to measure the remaining gap between the DTI washer protrusions and the bearing surface after a bolt is tensioned, confirming proper pretension.
How often should DTI washers be inspected?
Sample testing must be done for every new lot of fasteners. Field inspection frequency depends on project specifications, but typically requires checking a representative percentage of installed bolts.
Can I use any feeler gauge for DTI inspection?
No, you must use a gauge with the specific thickness designated by RCSC/ASTM standards (usually 0.015" for uncoated or 0.005" for coated DTIs).
What happens if a DTI washer fails inspection?
If the feeler gauge is not refused in enough gaps, the bolt is under-tensioned and must be further tightened until the proper gap is achieved.
Do Squirtern DTI washers require feeler gauge inspection?
While Squirtern DTIs provide a visual indication that reduces field feeler gauge checks, initial sample testing and periodic feeler gauge verification are still required to ensure compliance.
Where can I buy DTI washers with feeler gauges?
You can purchase them directly from FULLERKREG. Explore our Squirtern DTI washer collection or reach out to us at sales@fullerkr.com for quotes.
Ensure Flawless Connections with FULLERKREG
Streamline your structural steel inspections and eliminate guesswork on the job site.
Shop ASTM F959 Squirtern DTI Washers
For technical inquiries, documentation, or bulk orders, please contact sales@fullerkr.com.