ASME B18.2.2 Hex Coupling Nuts (Inch Series)
ASME B18.2.2 hex coupling nuts, inch series #6 – 6 in — the elongated hex nut that joins two threaded rods end-to-end or extends a stud, with the collected per-size table: width across flats and corners, thickness (roughly 1 x nominal diameter) and basic thread major diameter.
Last updated: 2026-11
Specifications
The hex coupling nut is the inch-system splice: a hex nut of roughly one nominal-diameter thickness that is threaded its full length so two studs or threaded rods can be screwed into it from both ends and joined in tension — rod-to-rod extensions, anchor-bolt adjusters, and any place a weld or coupling machining would be the alternative. Its thread length is what separates it from every other hex nut in B18.2.2: a standard hex nut threads only a few pitches deep, while a coupling nut is tapped through, so thread engagement is set by how far each rod is screwed in, not by the nut's height. The collected table runs #6 through 6 in — one of the widest size ladders on this site, because coupling nuts live in construction and utility work where large rod sizes are routine — and carries per size: basic major diameter of thread, width across flats F (basic/min/max), across corners G (min/max) and thickness H (basic/min/max). Thickness tracks the nominal size (1/2 in nut: 1 3/4 in thick; 2 in nut: 6 in thick), which is the dimension that gives the joint its engagement depth. Two reading notes live in the table footnotes: the source repeats its header block between column groups, and the 3 in row prints the across-flats basic as "4.5/8" — kept verbatim, read as 4 5/8 against its min/max cells. Property classes and finishes are not tabulated by the collected specification — per RFQ.
| Standard | ASME B18.2.2-2010 — square and hex nuts, inch series (hex coupling nut: full-length threaded elongated hex nut for joining threaded rod/stud end-to-end) |
|---|---|
| Size range | Nominal #6 – 6 in, thirty-six sizes in three source column groups (#6–1, 1 1/8–3, 3 1/4–6); threads per the UNC ladder of each size |
| Tabulated geometry | Per size: basic major dia. of thread, width across flats F (basic/min/max), width across corners G (min/max), thickness H (basic/min/max, e.g. 1/2 in: F 11/16 basic, H 1 3/4 basic / 1.690 min / 1.760 max) |
| Engagement | Threaded full length; engagement is set by rod insertion depth per end (source Note 1: nuts furnished without hole unless ordered; optional visual-aid hole at mid-nut thickness, 0.2–0.4 x nominal dia., or 1 in for 2 3/4 in and larger) |
| Property classes / finishes | Not tabulated by the collected specification — per RFQ (state grade and finish at quotation) |
| Nominal Size | Basic Major Dia. of Thread | F — Width Across Flats (basic) | F — Min. | F — Max. | G — Width Across Corners Min. | G — Max. | H — Thickness (basic) | H — Min. | H — Max. |
|---|---|---|---|---|---|---|---|---|---|
| #6 | 0.138 | 5/16 | 0.302 | 0.312 | 0.344 | 0.361 | 1/2 | 0.470 | 0.510 |
| #8 | 0.164 | 5/16 | 0.302 | 0.312 | 0.344 | 0.361 | 5/8 | 0.595 | 0.645 |
| #10 | 0.190 | 5/16 | 0.302 | 0.312 | 0.344 | 0.361 | 3/4 | 0.711 | 0.760 |
| 1/4 | 0.250 | 7/16 | 0.428 | 0.438 | 0.488 | 0.505 | 1 3/4 | 1.690 | 1.760 |
| 5/16 | 0.312 | 1/2 | 0.489 | 0.500 | 0.557 | 0.577 | 1 3/4 | 1.690 | 1.760 |
| 3/8 | 0.375 | 9/16 | 0.551 | 0.562 | 0.628 | 0.650 | 1 3/4 | 1.690 | 1.760 |
| 7/16 | 0.437 | 5/8 | 0.607 | 0.625 | 0.692 | 0.722 | 1 3/4 | 1.690 | 1.760 |
| 1/2 | 0.500 | 11/16 | 0.663 | 0.688 | 0.756 | 0.794 | 1 3/4 | 1.690 | 1.760 |
| 9/16 | 0.562 | 13/16 | 0.782 | 0.813 | 0.891 | 0.939 | 2 1/8 | 2.067 | 2.135 |
| 5/8 | 0.625 | 13/16 | 0.782 | 0.813 | 0.891 | 0.939 | 2 1/8 | 2.067 | 2.135 |
| 3/4 | 0.750 | 1 | 0.963 | 1.000 | 1.097 | 1.155 | 2 1/4 | 2.190 | 2.260 |
| 7/8 | 0.875 | 1 1/4 | 1.212 | 1.250 | 1.382 | 1.443 | 2 1/2 | 2.440 | 2.510 |
| 1 | 1.000 | 1 3/8 | 1.325 | 1.375 | 1.511 | 1.588 | 2 3/4 | 2.690 | 2.760 |
| 1 1/8 | 1.125 | 1 1/2 | 1.450 | 1.500 | 1.653 | 1.732 | 3 | 2.940 | 3.010 |
| 1 1/4 | 1.250 | 1 5/8 | 1.575 | 1.625 | 1.825 | 1.876 | 3 | 2.940 | 3.010 |
| 1 1/2 | 1.500 | 2 | 1.950 | 2.000 | 2.275 | 2.309 | 3 1/2 | 3.440 | 3.510 |
| 1 5/8 | 1.625 | 2 9/16 | 2.481 | 2.562 | 2.828 | 2.959 | 4 7/8 | 4.830 | 4.910 |
| 1 3/4 | 1.750 | 2 3/4 | 2.662 | 2.750 | 3.035 | 3.175 | 5 1/4 | 5.210 | 5.290 |
| 1 7/8 | 1.875 | 2 15/16 | 2.844 | 2.938 | 3.242 | 3.392 | 5 5/8 | 5.580 | 5.670 |
| 2 | 2.000 | 3 1/8 | 3.025 | 3.125 | 3.448 | 3.608 | 6 | 5.950 | 6.040 |
| 2 1/4 | 2.250 | 3 1/2 | 3.388 | 3.500 | 3.862 | 4.041 | 6 3/4 | 6.700 | 6.800 |
| 2 1/2 | 2.500 | 3 7/8 | 3.750 | 3.875 | 4.275 | 4.474 | 7 1/2 | 7.440 | 7.550 |
| 2 3/4 | 2.750 | 4 1/4 | 4.112 | 4.250 | 4.688 | 4.907 | 8 1/4 | 8.190 | 8.310 |
| 3 | 3.000 | 4.5/8 | 4.475 | 4.625 | 5.101 | 5.340 | 9 | 8.940 | 9.060 |
| 3 1/4 | 3.250 | 5 | 4.838 | 5.000 | 5.515 | 5.773 | 9 3/4 | 9.680 | 9.810 |
| 3 1/2 | 3.500 | 5 3/8 | 5.200 | 5.375 | 5.928 | 6.206 | 10 1/2 | 10.430 | 10.570 |
| 3 3/4 | 3.750 | 5 3/4 | 5.562 | 5.750 | 6.340 | 6.639 | 11 1/4 | 11.170 | 11.320 |
| 4 | 4.000 | 6 1/8 | 5.925 | 6.125 | 6.754 | 7.072 | 12 | 11.920 | 12.080 |
| 4 1/4 | 4.250 | 6 1/2 | 6.288 | 6.500 | 7.168 | 7.506 | 12 3/4 | 12.670 | 12.830 |
| 4 1/2 | 4.500 | 6 7/8 | 6.650 | 6.875 | 7.581 | 7.939 | 13 1/2 | 13.420 | 13.580 |
| 4 3/4 | 4.750 | 7 1/4 | 7.012 | 7.250 | 7.994 | 8.372 | 14 1/4 | 14.160 | 14.340 |
| 5 | 5.000 | 7 5/8 | 7.375 | 7.625 | 8.408 | 8.805 | 15 | 14.910 | 15.090 |
| 5 1/4 | 5.250 | 8 | 7.738 | 8.000 | 8.821 | 9.238 | 15 3/4 | 15.650 | 15.850 |
| 5 1/2 | 5.500 | 8 3/8 | 8.100 | 8.375 | 9.234 | 9.671 | 16 1/2 | 16.400 | 16.600 |
| 5 3/4 | 5.750 | 8 3/4 | 8.462 | 8.750 | 9.647 | 10.104 | 17 1/4 | 17.150 | 17.350 |
| 6 | 6.000 | 9 1/8 | 8.825 | 9.125 | 10.060 | 10.537 | 18 | 17.890 | 18.110 |
- Row 25 (3 1/4): The source repeats the full column-header block between column groups (before the 1 1/8 and 3 1/4 rows); duplicates are not reproduced as data. The 3 in. row prints the across-flats basic as '4.5/8' (read: 4 5/8, consistent with the min 4.475 / max 4.625 cells); kept verbatim.
Materials
- Material, property class and finish specified per RFQ — coupling nuts carry full rod load in tension, so grade matching to the rod matters; state the rod grade at quotation
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (ASME B18.2.2 Hex Coupling Nuts (Inch Series)) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 10,000 pieces. Stock items run 3–7 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
How much thread engagement does a coupling nut give, and what does the thickness dimension actually buy me?
Look at the H column: the basic thickness of a B18.2.2 coupling nut tracks its nominal diameter — a 1/2 in coupling nut is 1 3/4 in thick, a 1 in nut is 2 3/4 in, a 2 in nut is 6 in. Because the nut is tapped through, that thickness is pure available thread: screw a rod in halfway from each side and each rod gets roughly half the nut thickness of engagement — on the 1 in nut, about 1 3/8 in of thread per rod, or around twelve-plus full pitches of UNC thread. That is several times the engagement a standard hex nut offers, and it is the whole reason the part exists: the joint's tensile capacity becomes limited by the rod itself rather than by thread stripping in the nut. The collected table also carries the source's Note 1 on the optional inspection hole: on long couplings, installers cannot see whether each rod reached the middle, so the standard recommends a small drilled hole (0.2–0.4 x nominal diameter, or 1 in on sizes 2 3/4 and up) at mid-thickness as a visual check aid — orderable, but nuts come without it unless specified. Two quoting details: match the nut grade to the rod grade, since the coupling carries the full splice tension; and check the F column wrench sizes by row — the ladder is printed, not assumed from the nominal.
What is the MOQ and lead time for this nut type?
The minimum order quantity is 10,000 pieces. Stock items ship in 3–7 days; non-stock items are confirmed at quotation. Common sizes in this nut type are widely stocked; confirm the exact schedule against quantity and size mix at quotation.
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support