ASME B18.2.2 Square Nuts (Inch Series)
ASME B18.2.2 square nuts, inch series 1/4 – 1 1/2 in — the four-flat pattern paired with carriage bolts and square-head hardware, with the collected per-size table: width across flats and corners at basic/min/max and thickness at basic/min/max.
Last updated: 2026-11
Specifications
The square nut is the inch system's legacy pattern, and it survives because of what the four flats do that six cannot: a square nut resists turning to a flat in a square hole or chisel-cut slot, and it pairs with square-head bolts and carriage bolts where a wrench turns only to the next 90° face. The collected table runs 1/4 through 1 1/2 in and carries per size: width across flats F (basic/min/max), width across corners G (min/max) and thickness H (basic/min/max). The proportions differ from the hex pattern in ways that matter when substituting: across corners, a square nut reaches further (G = F × √2; the 1/2 in nut spans 0.788–0.812 across flats but 1.052–1.149 across corners, versus 0.840–0.866 corners for a 1/2 in hex nut), so on a tight corner-to-corner clearance the square pattern can foul where a hex fits. Thickness runs close to the hex nut's (1/2 in: 0.418–0.458 vs 0.427–0.448 hex). The F basic column reads as simple fractions — 7/16, 9/16, 5/8 — which is why square nuts still get cut into legacy wood and cast-iron work with period hardware. 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 (square nut: four-flat pattern for square-head and carriage-bolt assemblies) |
|---|---|
| Size range | Nominal 1/4 – 1 1/2 in, thirteen sizes (1/4, 5/16, 3/8 … 1 1/2); one geometry row per size; no machine screw sizes below 1/4 in the collected table |
| 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 13/16 basic (0.788–0.812), G 1.052–1.149, H 7/16 basic (0.418–0.458) |
| Proportions | Across corners G extends to F × √2 — further than a hex nut at the same thread; thickness H tracks the hex nut within a few thousandths across the ladder |
| 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 — Across Flats (basic) | F (min) | F (max) | G — Across Corners (min) | G (max) | H — Thickness (basic) | H (min) | H (max) |
|---|---|---|---|---|---|---|---|---|---|
| 1/4 | 0.2500 | 7/16 | 0.425 | 0.438 | 0.554 | 0.619 | 7/32 | 0.203 | 0.235 |
| 5/16 | 0.3125 | 9/16 | 0.547 | 0.562 | 0.721 | 0.795 | 17/64 | 0.249 | 0.283 |
| 3/8 | 0.3750 | 5/8 | 0.606 | 0.625 | 0.802 | 0.884 | 21/64 | 0.310 | 0.346 |
| 7/16 | 0.4375 | 3/4 | 0.728 | 0.750 | 0.970 | 1.061 | 3/8 | 0.356 | 0.394 |
| 1/2 | 0.5000 | 13/16 | 0.788 | 0.812 | 1.052 | 1.149 | 7/16 | 0.418 | 0.458 |
| 5/8 | 0.6250 | 1 | 0.969 | 1.000 | 1.300 | 1.414 | 35/64 | 0.525 | 0.569 |
| 3/4 | 0.7500 | 1 1/8 | 1.088 | 1.125 | 1.464 | 1.591 | 21/32 | 0.632 | 0.680 |
| 7/8 | 0.8750 | 1 5/16 | 1.269 | 1.312 | 1.712 | 1.856 | 49/64 | 0.740 | 0.792 |
| 1 | 1.0000 | 1 1/2 | 1.450 | 1.500 | 1.961 | 2.121 | 7/8 | 0.847 | 0.903 |
| 1 1/8 | 1.1250 | 1 11/16 | 1.631 | 1.688 | 2.209 | 2.386 | 1 | 0.970 | 1.030 |
| 1 1/4 | 1.2500 | 1 7/8 | 1.812 | 1.875 | 2.458 | 2.652 | 1 3/32 | 1.062 | 1.126 |
| 1 3/8 | 1.3750 | 2 1/16 | 1.994 | 2.062 | 2.708 | 2.917 | 1 13/64 | 1.169 | 1.237 |
| 1 1/2 | 1.5000 | 2 1/4 | 2.175 | 2.250 | 2.956 | 3.182 | 1 5/16 | 1.276 | 1.348 |
Materials
- Material, property class and finish specified per RFQ — state the mating bolt (square head or carriage bolt) with the order so the wrenching and bearing pattern matches
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 Square 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
Can I swap a hex nut for a square nut at the same thread size?
The thread will mate, but two dimensions decide whether the swap works, and both are on the collected tables. Across corners is the first check: the square nut's corners reach F × √2 — the 1/2 in square nut spans 1.052–1.149 in corner to corner while the 1/2 in hex nut reaches only 0.840–0.866 in — so in a recess or against adjacent hardware the square pattern can foul where the hex fit. Across flats is the second: the wrench sizes differ (1/2 in square: 13/16 basic; 1/2 in hex: 3/4 basic), and a square nut cannot be turned past 90° per wrench reposition, which matters in tight access — the hex pattern offers six positions, the square four. Where the square nut is genuinely the right answer it wins for positive reasons: it cannot rotate in a square hole or chisel slot, it is the period-correct partner for square-head machine bolts, and its simple fractional F basics (7/16, 9/16, 5/8 …) make it the pattern legacy drawings specify. Beyond geometry, do not carry an assumption across the swap: the hex nut page's proof-load grades are not tabulated for the square pattern by the collected specification, so state the required grade explicitly at quotation.
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