FULLERKREG® Direct Tension Indicators (DTI's) are the simplest, easiest to implement, and most cost-effective method for ensuring quality in bolt tightening operations. Compliant with ASTM F959 / F959M, RCSC, AASHTO, and FHWA specifications, FULLERKREG® DTI's use a patented orange silicone compound to provide instant visual confirmation of correct bolt preload — no feeler gage required.
Thinking that reaching the torque value means the bolt is properly tightened. Torque is a rotational force — the force required to rotate the nut along the bolt threads. You can apply a very high torque value to tighten a bolt without actually achieving proper tightness. On construction sites, many factors cause additional torque increase, such as dirt, dust, high temperatures, rust, rain, moisture, damaged threads, poor thread precision, excessive surface coating, improper storage, insufficient lubrication, and even issues with the torque tool itself.
Tension is the linear force generated when a bolt is stretched. The bolt’s elongation clamps two components together firmly. It is the true force that creates a solid joint. Tension is the actual goal of bolt tightening operations.
Standard Direct Tension Indicators (DTIs) are specially designed, stamped, heat-treated, coated, and tested washers featuring several semicircular raised protrusions (bumps). When used with high-strength bolts in steel structural connections, the tension gradually increases during tightening. The raised protrusions on the washer are compressed and gradually flattened by the pressure from above. When the blade of a feeler gage can no longer enter the gap and touches the bolt shank, it indicates that the deformation of the washer protrusions has reached the required amount (designed for a compression load equivalent to 70% of the bolt’s minimum tensile strength or minimum preload).
The Direct Tension Indicator is a displacement control method that directly responds to tension, free from the influence of thread conditions and other resistances that affect torque. Standard DTIs were developed in North America as early as the 1970s. However, because deformation verification and inspection still required the use of a feeler gage, they were not particularly convenient to use and therefore did not become widespread in steel structural bolting operations.
In 1996, FULLERKREG developed the FULLERKREG® Direct Tension Indicators (FULLERKREG® DTI's). This innovation fills the grooves on the backside of the protrusions with a soft orange silicone compound and incorporates discharge channels. When the washer protrusions are gradually flattened under load, the orange silicone compound is extruded through the channels and appears around the perimeter of the tension indicator. This allows the deformation of the tension indicator to be confirmed and inspected visually.
This innovative invention fully realizes the functionality and practicality of Direct Tension Indicators. FULLERKREG® Direct Tension Indicators make bolt tightening a simple and rapid operation: start turning the nut (bolt head)... tighten... when the appropriate amount of orange silicone compound (pre-calibrated to the required preload) extrudes around the indicator, stop turning the nut (bolt head)... correct bolt tensioning is complete.
Currently, there are four methods for applying preload to high-strength bolts: Calibrated Wrench, Turn-of-Nut, Torque Control Bolts, and Direct Tension Indicators. When used correctly, all four methods can produce the correct preload. However, except for FULLERKREG® Direct Tension Indicators, the others are all torque-based methods for bolt tightening, each with varying degrees of construction complexity and effectiveness differences. Steel construction professionals unanimously agree that FULLERKREG® Direct Tension Indicators are the most reliable and simplest of these methods for achieving correct preload.
Easier & Superior to Turn-of-Nut and Calibrated Wrench Methods
No need to mark or remember to stop tightening at 1/3, 1/2, or 2/3 turns. No need for daily or per-batch bolt condition and torque wrench verification or recalibration.
Superior to Torque Control Bolts
Direct tension control, not torque control. No special proprietary tightening tools required. No broken-off ends that become potential jobsite safety hazards and sources of bolt corrosion. No issues with the tail end breaking off due to torque before the steel components are joined.
Suitable for High-Strength Bolts of Any Length; Bolt Quality Inspection
Even for extremely short or long bolts, FULLERKREG® Direct Tension Indicators activate accurately when the tension value is reached. Derived inspection function — to examine bolt performance when pre-tension locking quality cannot be reached repeatedly or when there are doubts about bolt sourcing.
Prevents Excessive Torque, Accurately Controls Bolt Tightening
The installer knows exactly when to stop tightening. Some applications require bolts to be slightly tighter without over-tightening. FULLERKREG® Direct Tension Indicators achieve effective, accurate control that was previously impossible.
Achieves Optimal Snug-Tight Conditions
The orange silicone compound appears in trace amounts, small amounts, or full amounts (design preload), allowing bolt tightening status to be known and controlled. This facilitates completing correct tension on every bolt in sequence, achieving the most uniform and optimal bolt snug-tight condition and consistency across all bolt groups for the best steel assembly quality.
Simple Visual Direct Tension Indicator; Saves Construction Time
The orange silicone compound is easily identified visually. No other inspection tools are needed during installation; both novice and experienced installers can easily master it. Visual confirmation of locking tension shortens identification time and increases tool relocation speed, saving installation labor hours.
Safer for Inspectors
Inspectors (quality control checkers) can easily see the amount of orange silicone compound extruded from a distance to identify bolt tightening status. They do not need to carry inspection tools and climb up and down steel structures to personally inspect bolts at every joint, nor rely solely on initial feeler gage sampling of a few bolts. In fact, the adoption of FULLERKREG® Direct Tension Indicators allows every single bolt to be inspected.
| Application Requirement | Recommended Method |
|---|---|
| Visual confirmation required, no special tools | FULLERKREG® DTI (SquirternType) |
| Standard structural steel, torque wrench available | Calibrated Wrench or Turn-of-Nut |
| High-volume, speed-critical assembly | FULLERKREG® DTI (fastest inspection) |
| Wind turbine tower flange M36–M48 | FULLERKREG® DTI (GL Certified) |
| Bridge structural steel (FHWA / DOT projects) | FULLERKREG® DTI (FHWA compliant) |
| Bolt quality verification / sourcing audit | FULLERKREG® DTI (derived inspection function) |
FULLERKREG® ASTM F959 DTI Squirtern Washers — product range overview:
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FULLERKREG® Direct Tension Indicators are a product whose benefits are shared by every stakeholder involved in a structural steel project. From the engineer’s office to the inspector on the beam, every party gains measurably from correct, verifiable bolt tension.
🏗️ For Structural Engineers & Designers
Joint design is based on bolt tension — not torque. FULLERKREG® DTIs are the only bolt-tightening method that directly controls and verifies tension, the very parameter that joint design depends on. Engineers can confidently specify DTIs knowing that the installed bolt tension will match design intent.
🏢 For Building Owners & Facility Operators
Every bolt in the structure can be visually verified — not just a sample. FULLERKREG® DTIs allow 100% inspection of bolt tension at every joint without special instruments.
🔩 For Steel Fabricators & Steel Erectors
FULLERKREG® DTIs simplify shop and field bolting operations. No daily torque wrench calibration, no turn-of-nut marking, no proprietary breakaway tools. Multiple major erectors — including Dick Construction, V&M Erectors, Wood Hopkins Erectors, Babcock Wilcox Construction Company, Fluor Daniel Construction, and Bechtel Construction Company — have adopted FULLERKREG® DTIs as their standard method.
🏗️ For General Contractors & Structural Steel Contractors
FULLERKREG® DTIs reduce construction time and eliminate re-work from under- or over-tightened bolts. Visual confirmation is instant — inspectors do not need to physically access every joint with a feeler gage.
⚙️ For Equipment Manufacturers & OEM Suppliers
FULLERKREG® DTIs provide precise, repeatable tension control within ±10% of target preload (GL Certified for M36–M48 wind turbine flange connections). Leading OEMs including Siemens Westinghouse, Boeing, and FMC Jetway have confirmed that FULLERKREG® DTIs meet the precision requirements of their critical bolted connections.
📋 For EPC Contractors & Turnkey Project Managers
FULLERKREG® DTIs allow QA supervisors to verify 100% of structural bolts by visual walkdown. Major EPC firms — including Bechtel, Fluor Daniel, Foster Wheeler (Parsons), Black & Veatch, and Kellogg Brown & Root — have successfully implemented FULLERKREG® DTIs on projects where constructability and schedule reliability are paramount.
🔍 For Inspectors, QA/QC Teams & Certifying Authorities
FULLERKREG® DTIs transform bolt inspection from a sampling exercise into a 100% verification process. Inspectors can identify the tightening status of every bolt from a distance — trace silicone means snug-tight, partial extrusion means approaching preload, full extrusion means correct tension achieved.
FULLERKREG® Direct Tension Indicator Washers set the benchmark for bolt joint quality recognition across every discipline involved in structural steel construction.
“Because of the bolt location, the dedicated installation wrench could not be properly positioned and operated. We had to use an alternative wrench instead — but no matter how hard we tried, we could not get the orange silicone compound to extrude. Those two bolts were never fully tensioned.”
Without the orange silicone alert of FULLERKREG® Direct Tension Indicators, an undertightened bolt remains an undertightened bolt — invisible and undetected. This is precisely why FULLERKREG® DTIs are not simply a convenience — they are a structural safety safeguard.
| Carbon (C) | Manganese (Mn) | Phosphorus (P) | Sulfur (S) | Silicon (Si) |
|---|---|---|---|---|
| 0.30 – 0.55 | 0.50 – 0.90 | 0.04 Max | 0.045 Max | 0.15 – 0.35 |
| Nominal Bolt Diameter | Type A325 — Compression Load (000 lb) | Type A490 — Compression Load (000 lb) | Note | |||||
|---|---|---|---|---|---|---|---|---|
| Load Range | Black Oxide | Mech. Galv. | Weathering Steel | Load Range | Black Oxide | Qty/Pail & Wt | ||
| 1/2" (12.700 mm) | 12 – 14 | ✓ | ✓ | N/A | 15 – 18 | ✓ | 1,750 pcs / 50 lb | |
| 5/8" (15.875 mm) | 19 – 23 | ✓ | ✓ | N/A | 24 – 29 | ✓ | 1,250 pcs / 60 lb | |
| 3/4" (19.050 mm) | 28 – 34 | ✓ | ✓ | ✓ | 35 – 42 | ✓ | 750 pcs / 60 lb | |
| 7/8" (22.225 mm) | 39 – 47 | ✓ | ✓ | ✓ | 49 – 59 | ✓ | 500 pcs / 60 lb | |
| 1" (25.400 mm) | 51 – 61 | ✓ | ✓ | ✓ | 64 – 77 | ✓ | 400 pcs / 60 lb | |
| 1 1/8" (28.575 mm) | 56 – 67 | ✓ | ✓ | N/A | 80 – 96 | ✓ | 350 pcs / 60 lb | |
| 1 1/4" (31.750 mm) | 71 – 85 | ✓ | ✓ | N/A | 102 – 122 | ✓ | 250 pcs / 60 lb | |
| 1 3/8" (34.925 mm) | 85 – 102 | ✓ | ✓ | N/A | 121 – 145 | N/A | 175 pcs / 60 lb | |
| 1 1/2" (38.100 mm) | 103 – 124 | ✓ | ✓ | N/A | 148 – 178 | ✓ | 175 pcs / 60 lb | Offer M36 10.9 |
| Nominal Bolt Diameter | Type 8.8 — Compression Load (kN) | Type 10.9 — Compression Load (kN) | Note | |||||
|---|---|---|---|---|---|---|---|---|
| Load Range | Black Oxide | Mech. Galv. | Weathering Steel | Load Range | Black Oxide | Qty/Pail & Wt | ||
| M16 | 91 – 109 | ✓ | ✓ | N/A | 114 – 131 | ✓ | 1,250 pcs / 60 lb | |
| M20 | 142 – 170 | ✓ | ✓ | N/A | 179 – 206 | ✓ | 750 pcs / 60 lb | |
| M22 | 176 – 211 | ✓ | ✓ | N/A | 221 – 254 | ✓ | 650 pcs / 60 lb | |
| M24 | 205 – 246 | ✓ | ✓ | N/A | 257 – 296 | ✓ | 450 pcs / 60 lb | |
| M27 | 267 – 320 | ✓ | ✓ | N/A | 334 – 384 | ✓ | 325 pcs / 60 lb | |
| M30 | 326 – 391 | ✓ | ✓ | N/A | 408 – 469 | ✓ | 250 pcs / 60 lb | |
| M36 | 475 – 570 | ✓ | ✓ | N/A | 595 – 684 | ✓ | 175 pcs / 60 lb | |
| M42, M48, M56, M64 — Special Order (Special strength — Suit DIN 6914 Grade 10.9 and DIN 18800) | ||||||||
Line Card Notes: (1) Manufactured to ASTM F959/F959M. (2) Compression load is proportional to bolt tension; each lot tested at 0.005" or 0.015" feeler gage clearance; min load = 70% of bolt min tensile strength; max = 20% above min. (3) N/A = non-stock; special coatings (Dacromet, Xylan) and sizes available on request with MOQ.
| Bolt Diameter | Type A325 | Type A490 | A325 or A490 | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Max O.D. (C) | Bumps | Thickness (D) | Max O.D. (C) | Bumps | Thickness (D) | Hardness (Rc) | Min I.D. (A) | PTD (B) | |
| 1/2" | 1.187 (30.15) | 4 | 0.12 (3.05) | 1.375 (34.93) | 5 | 0.12 (3.05) | 32 | 0.527 (13.34) | 0.788 (20.16) |
| 5/8" | 1.375 (34.93) | 4 | 0.14 (3.56) | 1.625 (41.28) | 5 | 0.14 (3.56) | 32 | 0.658 (16.71) | 0.956 (24.28) |
| 3/4" | 1.625 (41.28) | 5 | 0.14 (3.56) | 1.750 (44.45) | 6 | 0.14 (3.56) | 32 | 0.790 (20.07) | 1.125 (28.58) |
| 7/8" | 1.875 (47.63) | 5 | 0.16 (4.06) | 2.000 (50.80) | 6 | 0.16 (4.06) | 32 | 0.921 (23.39) | 1.294 (32.87) |
| 1" | 2.000 (50.80) | 6 | 0.18 (4.57) | 2.250 (57.15) | 7 | 0.18 (4.57) | 32 | 1.052 (26.72) | 1.463 (37.16) |
| 1 1/8" | 2.250 (57.15) | 6 | 0.18 (4.57) | 2.500 (63.50) | 7 | 0.18 (4.57) | 32 | 1.183 (30.05) | 1.631 (41.43) |
| 1 1/4" | 2.480 (62.70) | 7 | 0.18 (4.57) | 2.750 (69.85) | 8 | 0.18 (4.57) | 32 | 1.315 (33.40) | 1.800 (45.72) |
| 1 3/8" | 2.750 (69.85) | 7 | 0.18 (4.57) | 3.000 (76.20) | 8 | 0.18 (4.57) | 32 | 1.446 (36.73) | 1.969 (50.01) |
| 1 1/2" | 3.000 (76.20) | 8 | 0.18 (4.57) | 3.250 (82.55) | 9 | 0.18 (4.57) | 32 | 1.557 (39.55) | 2.138 (54.31) |
| Bolt Diameter | Type Gr 8.8 | Type Gr 10.9 | Gr 8.8 or Gr 10.9 | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Max O.D. (C) | Bumps | Thickness (D) | Max O.D. (C) | Bumps | Thickness (D) | Hardness (Rc) | Min I.D. (A) | PTD (B) | |
| M16 | 36 | 4 | 3.4 | 36 | 4 | 3.8 | 32 | 17 | 25 |
| M20 | 46 | 5 | 3.8 | 46 | 6 | 3.8 | 32 | 21 | 29 |
| M22 | 50 | 5 | 3.8 | 50 | 6 | 4.3 | 32 | 23 | 33 |
| M24 | 55 | 5 | 4.4 | 55 | 6 | 4.4 | 32 | 25 | 38 |
| M27 | 61 | 6 | 4.4 | 62 | 7 | 4.4 | 32 | 28 | 43 |
| M30 | 68 | 7 | 4.4 | 69 | 8 | 5.2 | 32 | 32 | 47 |
| M36 | 81 | 8 | 5.0 | 83 | 9 | 5.2 | 32 | 38 | 56 |
Dimensional Notes: (1) Manufactured to ASTM F959/F959M. (2) The bolt head or hardened flat washer bearing against the DTI protrusions must have a hardness of at least Rockwell Rc 38. PS: Non-standard sizes available upon request.
In accordance with ASTM F959/F959M and RCSC specifications, a pre-installation verification test must be performed for each combination of bolt assembly and DTI washer before field installation begins. The purpose is to confirm that the specific bolt assembly will achieve the required minimum preload when the orange silicone compound is fully extruded from all protrusions of the DTI washer.
Skidmore Verification Procedure:
Using a Skidmore-Wilhelm bolt tension calibrator (or equivalent approved device), assemble the bolt, nut, and DTI washer in the calibrator following the same orientation and conditions as will be used in the structural connection. Tighten the bolt gradually. Observe the extrusion of the orange silicone compound from the protrusions. The minimum bolt tension required under RCSC for the applicable bolt diameter and grade must be achieved at or before the orange silicone compound is fully extruded from all protrusions. A minimum of three assemblies per lot must be tested. If all three tests pass, the lot is approved for installation. If any test fails, the lot must be rejected or re-evaluated.
ASTM A325 / A490 & Metric Grade 8.8 / 10.9 — Pre-Installation Verification Requirements:
The minimum bolt tension values used for verification shall conform to the applicable RCSC or AISC specification table for the bolt diameter and grade being used. The verification test confirms that the DTI washer is correctly calibrated to the bolt assembly in use, accounting for variables such as nut factor, lubrication condition, thread class, and bolt length.
Note: Verification must be repeated whenever there is a change in bolt lot, nut lot, washer lot, lubricant, or installation procedure.
DTI squirtern washers must be installed with the protrusion (bump) side facing the bolt head or a hardened flat washer. The silicone discharge channels must face outward so that extrusion can be observed visually during and after tightening.
Step-by-step installation procedure:
Important installation notes:
One of the most significant advantages of FULLERKREG® DTI Squirtern Washers is that inspection is entirely visual — no feeler gage, no torque wrench, and no physical access to each individual bolt is required for the primary acceptance check.
Acceptance criteria — visual inspection:
Additional inspection notes:
FULLERKREG Fasteners — Precision ASTM and Structural Fastener Solutions, Direct from Manufacturer.
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