ASME B18.2.6-2010 — Fasteners for Use in Structural Applications

🔩 ASME B18.2.6-2010 is the comprehensive standard for the fastener system of steel-structure connections, covering complete general and dimensional data for five inch-series structural fastener products. By bringing bolts, nuts, washers, and tension-indicating devices into one system, it serves as the authoritative reference for the design, procurement, erection, and inspection of structural connections. All dimensions are in inches unless otherwise stated and apply to unplated or uncoated product.

1. The Five Products Covered 📌

The Standard covers dimensional data for the following five structural fastener products:

• Heavy Hex Structural Bolts: ASTM A 325 and ASTM A 490.
• Heavy Hex Nuts: ASTM A 563 and ASTM A 194.
• Hardened Steel Washers: circular, circular clipped, and beveled — ASTM F 436.
• Compressible Washer-Type Direct Tension Indicators (DTI): ASTM F 959.
• Twist-Off-Type Tension Control Structural Bolts: heavy hex and round head configurations — ASTM F 1852 and ASTM F 2280.

2. Dimensions and Units 📏

The opening sections of the Standard set out the dimensional conventions:

• All dimensions are in inches unless otherwise stated, and apply to unplated or uncoated product; where plating or coating is specified, finished dimensions are as agreed between supplier and purchaser.
• Symbols specifying geometric characteristics are per ASME Y14.5.
• Options are at the discretion of the supplier unless otherwise agreed in the purchase order.
• Terminology refers to ASME B18.12; referenced standards (e.g., ASME B1.1, B1.2, B1.3, B18.2.1, B18.2.2) take their most recent issue at time of order placement.

3. Heavy Hex Structural Bolts and Mating Nuts 🔧

The Standard specifies, in turn:

• Heavy hex structural bolts (Table 1): width across flats, head height, thread length for each nominal diameter; Table 2 gives maximum grip gaging lengths and minimum body lengths to match thread and grip.
• Heavy hex nuts (Table 3): thickness and across-flats for structural use, with nut grades matched to bolt strength (e.g., Grade 2H).
• Hardened steel washers (Tables 4, 5): dimensions of circular and circular-clipped washers plus beveled washers with a 1:6 slope in thickness, used to compensate flange slope.

4. Direct Tension Indicators and Twist-Off Bolts 📏

• Direct tension indicators (Table 6): compressible washers with raised protrusions. As the bolt is tightened, the protrusions flatten; checking the gap with feeler gages shows whether the required preload has been reached — a simple and reliable tension-control means.
• Twist-off tension control bolts (Table 7): the bolt tail ends in a splined “point”; during tightening with a special wrench, the spline shears at a groove once the design preload is reached, providing both tension control and tamper evidence. The Standard specifies the groove diameter (Figure 1) and body/thread dimensions.

5. Engineering Practice Essentials 🛠️

• 🔍 Selection workflow: establish joint type (slip-critical vs. bearing) and design preload → select bolt grade (A325/A490) and size → match heavy hex nuts and hardened washers → choose tension-control method (torque, turn-of-nut, DTI, or twist-off).
• 🔧 Preload control: with DTI, check gap acceptance values per ASTM F 959; for twist-off bolts, the sheared spline indicates preload, but random verification is still required.
• 📊 Erection notes: slip-critical faying surfaces need slip treatment and timely tightening; use beveled washers on sloped flanges to keep the nut bearing face perpendicular to the bolt axis.
• 📋 Inspection: verify dimensions per the Standard’s tables, materials per the ASTM specs, and sample-check torque/tension of high-strength bolt assemblies.

6. Frequently Asked Questions ❓