A 3/4 heavy hex nut is 1-1/4 in across flats and 47/64 in thick; a 1 in nut is 1-5/8 across flats. The quickest field check: a heavy hex nut is about as thick as its own diameter and 1/8 in wider than the standard pattern — that is where the extra thread engagement on structural and pressure joints comes from. Full chart below, then the part tables never explain: what A563, A194 2H and A325 mean for the nut you actually order.
The heavy hex nut sizes below run 3/8 to 4 in. Width across flats F is the basic (max) figure — it is also the socket size. Across corners is the max figure. Thickness is the basic figure with decimal equivalent. Weights are approximate, per nut, for steel.
| Nominal size | Across flats F (socket) | Across corners, in | Thickness H | Weight | Bar stock to machine |
|---|---|---|---|---|---|
| 3/8 | 11/16 (0.688) | 0.794 | 23/64 (0.359) | 0.03 lb / 0.01 kg | 1.00 in |
| 1/2 | 7/8 (0.875) | 1.010 | 31/64 (0.484) | 0.07 lb / 0.03 kg | 1.25 in |
| 5/8 | 1-1/16 (1.062) | 1.227 | 39/64 (0.609) | 0.12 lb / 0.05 kg | 1.25 in |
| 3/4 * | 1-1/4 (1.250) | 1.443 | 47/64 (0.734) | 0.20 lb / 0.09 kg | 1.50 in |
| 7/8 | 1-7/16 (1.438) | 1.660 | 55/64 (0.859) | 0.30 lb / 0.14 kg | 1.75 in |
| 1 | 1-5/8 (1.625) | 1.876 | 63/64 (0.984) | 0.43 lb / 0.20 kg | 2.00 in |
| 1-1/8 | 1-13/16 (1.812) | 2.093 | 1-7/64 (1.109) | 0.59 lb / 0.27 kg | 2.25 in |
| 1-1/4 | 2 (2.000) | 2.309 | 1-7/32 (1.219) | 0.79 lb / 0.36 kg | 2.50 in |
| 1-3/8 | 2-3/16 (2.188) | 2.526 | 1-11/32 (1.344) | 1.02 lb / 0.46 kg | 2.75 in |
| 1-1/2 | 2-3/8 (2.375) | 2.742 | 1-15/32 (1.469) | 1.31 lb / 0.59 kg | 2.75 in |
| 1-3/4 | 2-3/4 (2.750) | 3.175 | 1-23/32 (1.719) | 2.04 lb / 0.93 kg | 3.25 in |
| 2 | 3-1/8 (3.125) | 3.608 | 1-31/32 (1.969) | 2.99 lb / 1.36 kg | 3.75 in |
| 2-1/4 | 3-1/2 (3.500) | 4.041 | 2-13/64 (2.203) | 4.19 lb / 1.90 kg | 4.25 in |
| 2-1/2 | 3-7/8 (3.875) | 4.474 | 2-29/64 (2.453) | 5.64 lb / 2.56 kg | 4.50 in |
| 3 | 4-5/8 (4.625) | 5.340 | 2-61/64 (2.953) | 9.50 lb / 4.31 kg | 5.50 in |
| 3-1/2 | 5-3/8 (5.375) | 6.207 | 3-7/16 (3.438) | 15.26 lb / 6.92 kg | 6.25 in |
| 4 | 6-1/8 (6.125) | 7.073 | 3-15/16 (3.938) | 21.80 lb / 9.89 kg | 7.25 in |
* The 3/4 size is the workhorse of bolted structural steel — if you are checking one nut on site, it is probably this row. Bar stock is the across-corners figure rounded up to the next 1/4 in stock size for clean-up — the max column already equals the sharp-corner distance F × 1.1547.
Heavy hex proportions follow two rules worth memorising: across flats = 1½ × diameter + 1/8 in, and thickness ≈ the nominal diameter (within 1/32 in up to 2 in; the largest sizes run up to 1/16 in under). A standard hex nut is 1/8 in narrower and noticeably thinner — the two patterns are not interchangeable on a specified joint, even when the thread matches.
Heavy hex is a shape; the grade is the metallurgy. Three designations cover almost every heavy hexagonal nut bought in North America, and they answer the question that matters: which nut goes on which bolt.
| Grade | What it is | Pairs with |
|---|---|---|
| ASTM A563 grade A | Plain carbon steel, the commercial grade | General fastening, A307 bolts — the default when a drawing just says “steel hex nut, heavy pattern” |
| ASTM A563 grade DH | Quenched and tempered | A325 and A490 structural bolts — the grade the structural code actually names |
| ASTM A194 grade 2H | Quenched and tempered, proof-tested at 175,000 psi | A193 B7 stud bolts on pressure flanges — and an accepted substitute for DH on structural joints |
Material beyond the carbon-steel grades: 304 and 316 stainless heavy hex nuts are machined for washdown and marine service (grade markings per ASTM F594, strength well below 2H — do not substitute on a loaded joint). 6061 or 7075 aluminium in the heavy hex pattern is a contradiction we will talk you out of: the pattern exists to add strength and bearing area, and an aluminium nut gives both away — where weight rules, a standard-pattern nut in 7075 serves better.
When a drawing says only “structural nut” with no grade, DH is the safe reading — it is the grade the structural code names. The practical consequence either way: one A194 2H nut covers both requirements. When A325 nuts are quoted long, 2H is the substitution the standard itself allows — and because 2H moves in pipeline volume, it is often the easier grade to find. What does not work is the reverse: an unmarked commercial nut on a structural or flanged joint fails inspection on the marking alone.
EKINSUN LTD is a custom parts manufacturer — heavy hex and large nuts are machined here from bar, one piece up, to ASME B18.2.2 or to your dimension. That cuts both ways, so the table is honest about it. One neighbouring family needs no machining at all: metric coupling nuts M4–M24 sit on our own stock shelf, hex and round, 12–70 mm long.
| What you need | In the catalogue? | What we machine |
|---|---|---|
| 1/2–1-1/2 in UNC, A563 grade A or 2H, plain or hot-dip galvanized | Yes — genuinely stocked | Buy it from stock. On a stocked structural size no one-off can match that price, and we will say so in the quote instead of taking the order. |
| 8UN thread series above 2 in — 2-1/4, 2-1/2, 3 in and up | Thin stock, long waits | Machined from bar to ASME B18.2.2 with the 8-pitch thread single-pointed. The big-bore flange sizes distributors quote in weeks, cut in days. |
| A194 2H properties on a metric thread — M30, M36, M30×1.5 | No — the standards do not cross | A 2H-grade body with the metric thread your studs actually carry. An M30 nut to heavy hex proportions, or the M30×1.5 fine-pitch nut no table lists — same lathe, same day. |
| Left-hand thread in any heavy hex size | No | Same operation, opposite lead — no extra tooling, no surcharge for the hand of thread. |
| Special width across flats — a hex your spanner or socket actually fits | No — the standard fixes the hex | Milled to your across-flats dimension. Common on retrofits where the standard 1-5/8 hex fouls the housing. |
| Oversize-tapped nuts for hot-dip galvanized studs, non-catalogue diametral allowance | Standard allowances only | Tapped to the allowance your coating actually measures, then gauged against your stud — not against a table. |
| A heavy hexagonal nut you cannot identify — worn, seized, or metric-imperial hybrid | No | Send the nut or the stud it runs on. We measure thread, pitch, across-flats and thickness, and reproduce it — no part number needed. |
A 3/4 heavy hex nut to ASME B18.2.2 measures 1-1/4 in across flats, 1.443 in across corners and 47/64 in (0.734 in) thick, and weighs about 0.20 lb (90 g). It takes a 1-1/4 in socket. Machining one from round bar takes 1.50 in stock. EKINSUN LTD machines 3/4 heavy hex nuts in UNC, UNF, 8UN or a metric thread, from one piece.
A 1 in heavy hex nut is 1-5/8 in across flats, 1.876 in across corners and 63/64 in (0.984 in) thick — within 1/64 in of its nominal diameter, which is the quickest way to tell a heavy hex nut from a standard one. It weighs about 0.43 lb (195 g) and takes a 1-5/8 in socket. From bar, it needs 2.00 in stock.
A 2 in heavy hex nut is 3-1/8 in across flats, 3.608 in across corners and 1-31/32 in thick, and weighs about 2.99 lb (1.36 kg). It takes a 3-1/8 in socket and needs 3.75 in bar stock to machine. At this size the stocked thread is 4-1/2 UNC (4.5 threads per inch) or 8UN — anything else is a machined part.
An ASTM A563 grade DH heavy hex nut, or an ASTM A194 grade 2H — the specification lists 2H as an acceptable substitute for DH, and in practice 2H is often easier to source. Both are quenched-and-tempered steel nuts in heavy hex proportions. A standard-pattern steel hex nut of unstated grade is not an acceptable pairing on a structural joint.
Grade 2H is ASTM A194's quenched-and-tempered carbon steel class, proof-tested at 175,000 psi. It was written for pressure and temperature service — the nuts that run on A193 B7 stud bolts in flanged joints — and because its strength covers A563 DH, one 2H nut stocks out both the structural and the piping requirement.
Metric sizes live on their own chart: large hex nut dimensions M56–M160 — DIN 934 across flats, height, weight and which fine pitches exist. For the bolts these nuts run on, see heavy hex & structural bolts M20–M100 and the family head, hex bolts & hex head bolt dimensions.
A heavy hex nut is 1/8 in wider across flats than a standard (finished) hex nut of the same thread, and thicker — its thickness runs within 1/32 in of the nominal diameter up to 2 in (the largest sizes run up to 1/16 in under), where a standard nut is about 7/8 of the diameter. The extra width and height put more thread in engagement and more bearing surface under load, which is why structural steel and pressure-flange joints specify heavy hex nuts and not steel hex nuts of the ordinary pattern.
A563 grade A is the plain commercial grade for general fastening. A563 DH is quenched and tempered, and is the structural grade that ASTM A325 bolts specify. A194 2H is the pressure-piping grade for A193 B7 studs, proof-tested at 175,000 psi — and since it meets or exceeds DH, it is an accepted substitute on structural joints. If your drawing names A325 or A490 bolts, price DH and 2H both.
Effectively yes. Up to about 1-1/2 in UNC, heavy hex nuts in A563 A and 2H are genuine shelf items. Above 2 in, and in the 8UN thread series the large flange sizes use, stock thins to a few distributors and lead times stretch — those are the sizes we machine from bar. The same applies to any big hex nut in a thread the catalogue never carried: metric heavy hex, left-hand, or fine pitch.
Yes — that hybrid is a real and recurring need: plants running metric studs with imperial sockets, or an M30 nut needed in heavy hex proportions for bearing area. The hex is milled to either the metric or the inch across-flats table, and the thread is single-pointed to M30, M36, M30×1.5 or whatever the stud carries. No standard covers it, which is exactly why it cannot be bought.
Yes. The zinc on the bolt thread takes up clearance, so galvanized heavy hex nuts are tapped with a diametral allowance after coating considerations — which is why a galvanized nut runs loose on a plain bolt. When we machine nuts for galvanized studs we tap to the allowance the coating actually measures and gauge against your stud, not against a generic table.
EKINSUN LTD is a custom parts manufacturer: heavy hex nuts and large hex nuts from 3/8 in to 4 in and M30 to M160, in 8UN, UNC, UNF, metric coarse or fine pitch, either hand of thread, from a drawing, a sketch or the worn nut itself. MOQ 1, quote in 12 hours. For the stocked structural sizes, we will tell you to buy from a distributor instead.
8UN over 2 in, metric-thread heavy hex, left-hand, special across-flats — machined to your drawing or from your old nut. MOQ 1, quote in 12 hours. For a custom metric nut — special form, class matched to your bolt — see large custom nuts.