Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
ASME B18.2.1 Hex Flange Screws
Hex bolts featuring an integrated circular flange that acts as a built-in washer, optimizing load distribution and accelerating assembly processes.
ASME B18.2.1 Hex Flange Screws combine a standard hexagonal head with a wide, circular flange at the base, effectively integrating the function of a washer into the fastener itself. This design eliminates the need for a separate flat washer, reducing part count, speeding up assembly time, and preventing the loss of washers during installation. The flange increases the bearing surface area significantly, which helps distribute the clamping load more evenly and prevents damage to softer mating surfaces. Some variants feature a serrated underside on the flange to provide a locking action against vibration, though the standard ASME B18.2.1 specification primarily covers the dimensional aspects of the smooth flange type. These screws are widely used in the automotive industry, appliance manufacturing, and general machinery where efficient, reliable, and vibration-resistant fastening is required.
ASME B18.2.1 Hex Flange Screws Dimensions (mm)
| Nominal Size (Ref Inch) | Body Diam., E | Width Across Flats, F | Width Across Corners, G | Maximum Flange Diam., B | Minimum Flange Thickness, K | Maximum Head Height, H | Minimum Hex Height, H1 | Maximum Flange Top Radius, R2 | Minimum Bearing Diam., B1 | Maximum Runout of Bearing Surface FIM | Basic Thread Length, LT | Maximum Transition Thread Length, Y | Ring T | Ring B | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Max. | Min. | Basic (Ref) | Max. | Min. | Max. | Min. | For Screws With L ≤ 152.4mm | For Screws With L > 152.4mm | For Screws With L ≤ 152.4mm | For Screws With L > 152.4mm | Inside Diameter | Inside Diameter | Thickness | |||||||||
| 1/4 | 0.2500 | 6.350 | 6.223 | 9.525 | 9.525 | 9.322 | 10.998 | 10.389 | 14.224 | 1.016 | 7.112 | 4.318 | 0.381 | 12.192 | 0.254 | 19.050 | 25.400 | 10.160 | 16.510 | 10.396 | 11.125 | 3.012 |
| 5/16 | 0.3125 | 7.938 | 7.785 | 12.700 | 12.700 | 12.421 | 14.656 | 13.919 | 17.272 | 1.270 | 8.128 | 5.334 | 0.483 | 15.240 | 0.279 | 22.225 | 28.575 | 10.592 | 16.942 | 13.927 | 14.783 | 3.701 |
| 3/8 | 0.3750 | 9.525 | 9.373 | 14.288 | 14.288 | 13.995 | 16.510 | 15.697 | 20.574 | 1.524 | 9.906 | 6.350 | 0.559 | 18.542 | 0.305 | 25.400 | 31.750 | 11.125 | 17.475 | 15.705 | 16.637 | 4.392 |
| 7/16 | 0.4375 | 11.113 | 10.935 | 15.875 | 15.875 | 15.545 | 18.339 | 17.399 | 23.622 | 1.778 | 11.684 | 7.620 | 0.660 | 21.590 | 0.330 | 28.575 | 34.925 | 11.786 | 18.136 | 17.407 | 18.542 | 5.334 |
| 1/2 | 0.5000 | 12.700 | 12.522 | 19.050 | 19.050 | 18.694 | 21.996 | 20.955 | 27.178 | 2.032 | 12.954 | 8.636 | 0.762 | 24.892 | 0.356 | 31.750 | 38.100 | 12.217 | 18.567 | 20.963 | 22.225 | 6.022 |
| 9/16 | 0.5625 | 14.288 | 14.084 | 20.638 | 20.638 | 20.269 | 23.825 | 22.733 | 30.226 | 2.286 | 14.478 | 9.652 | 0.864 | 27.940 | 0.381 | 34.925 | 41.275 | 19.050 | 19.050 | 22.741 | 24.130 | 6.713 |
| 5/8 | 0.6250 | 15.875 | 15.672 | 23.813 | 23.813 | 23.419 | 27.508 | 26.264 | 33.782 | 2.540 | 15.748 | 10.668 | 0.965 | 31.242 | 0.432 | 38.100 | 44.450 | 19.634 | 19.634 | 26.271 | 27.813 | 7.402 |
| 3/4 | 0.7500 | 19.050 | 18.821 | 28.575 | 28.575 | 27.940 | 32.995 | 31.344 | 40.386 | 2.794 | 18.542 | 12.954 | 1.143 | 37.338 | 0.508 | 44.450 | 50.800 | 20.320 | 20.320 | 31.351 | 33.325 | 9.035 |
ASME B18.2.1 Hex Flange Screws Length Tolerance (mm)
| Nominal Length | Nominal Size (inches) | |||||
|---|---|---|---|---|---|---|
| 1/4 to 3/8 | 7/16 and 1/2 | 9/16 to 3/4 | 7/8 and 1 | 1 1/8 to 1 1/2 | Over 1 1/2 | |
| Up to 25.4 mm, incl. | +0.000 0.762 |
+0.000 0.762 |
+0.000 0.762 |
... | ... | ... |
| Over 25.4 mm to 63.5 mm, incl. | +0.000 1.016 |
+0.000 1.524 |
+0.000 2.032 |
+0.000 2.540 |
+0.000 3.048 |
+0.000 4.572 |
| Over 63.5 mm to 101.6 mm, incl. | +0.000 1.524 |
+0.000 2.032 |
+0.000 2.540 |
+0.000 3.556 |
+0.000 4.064 |
+0.000 5.080 |
| Over 101.6 mm to 152.4 mm, incl. | +0.000 2.540 |
+0.000 2.540 |
+0.000 2.540 |
+0.000 4.064 |
+0.000 4.572 |
+0.000 5.588 |
| Longer than 152.4 mm | +0.000 4.572 |
+0.000 4.572 |
+0.000 4.572 |
+0.000 5.080 |
+0.000 5.588 |
+0.000 6.096 |
Frequently Asked Questions
- What does ASME B18.2.1 hex flange screws cover?
- ASME B18.2.1 is the inch dimensional standard for hex flange screws. It defines head dimensions, body diameter, thread length, total length, drive recess, and tolerances so any compliant hex flange screws interchanges with standard nuts, washers and wrenches across manufacturers.
- What size range is available for hex flange screws under ASME B18.2.1?
- hex flange screws under ASME B18.2.1 covers 1/4 in to 1 1/2 in nominal diameter with integral washer flange. TorqBolt manufactures the full range in ASTM A193 Grades B7, B7M, B8, B8M and the full ASTM A320 cryogenic counterpart on customer specification.
- What is the metric/inch counterpart of ASME B18.2.1 hex flange screws?
- The companion specification for hex flange screws is ASME B18.2.3.4M metric flange. Both standards share equivalent functional dimensions but use the corresponding measurement system (inch vs metric ISO M-series).
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