Hex Nut Dimensions Calculator

Across flats, across corners, thickness and bearing-face diameter for ISO 4032 style 1, ISO 4033 style 2, ISO 4035 thin, the legacy DIN 934, DIN 935 castle nuts and both nylon-insert forms — with the ISO 898-2 style each height qualifies as, computed from the standard’s own 0.45 D / 0.80 D / 0.90 D boundaries, and the contact pressure the bearing face puts on the member. DIN 934 turns out to be under the style 1 floor at every size from M5 up except M12.

Height, bearing face, and the ratio that names the style

The three ISO styles at the same thread size

DIN 934 against ISO 4032 — and the change the brief for this page did not mention

Nut property class against bolt property class — ISO 898-2 Table 2

Prevailing-torque nuts, and the pairing that is usually printed wrong

What this page will not compute, and where it is done

Thickness is the property class, and DIN 934 does not reach it

A nut’s thickness is not a detail; it is the property class. ISO 898-2 does not define its three nut styles by a picture, it defines them by the minimum height as a fraction of the thread diameter — style 0 is a thin nut with 0.45 D ≤ m_min < 0.80 D, style 1 is a regular nut with m_min ≥ 0.80 D, style 2 is a high nut at about 0.90 D. Take the three published dimension tables and compute those ratios and every row lands in its own band: ISO 4035 between 0.45 and 0.49, ISO 4032 between 0.80 and 0.88, ISO 4033 between 0.89 and 0.98. The standard and the dimension tables agree exactly, which is a nice thing to be able to check. Two rows fall outside: ISO 4032 M3 and M4 at 0.717 D and 0.725 D, because ISO 898-2’s scope starts at M5.

Apply the same test to DIN 934 and something falls out that the usual account of these standards does not mention. Everybody knows ISO 4032 changed the across-flats at four sizes. What is less often said is that it also raised the HEIGHT at every size from M5 up — M16 from 13 mm to 14.8, M20 from 16 to 18 — leaving only M3 and M4 alone. Compute DIN 934’s m_min ÷ D and the reason appears: it is BELOW 0.80 at every size from M5 up except M12. 0.740 at M5, 0.764 at M10, 0.769 at M16, 0.738 at M24. By ISO 898-2’s own definition a DIN 934 nut is not a style 1 nut. Würth put the consequence in terms: nuts to ISO 4032 “may not be replaced by nuts according to DIN standards which only have got a reduced loadability according to DIN 267 Part 4 … such as DIN 934”. Two differences, not one, and the second has a proof load attached to it.

Why style 2 exists is the same argument seen from the other side. The design intent behind ISO 898-2’s whole pairing table is that the nut’s proof load must exceed the bolt’s tensile strength, so that an overloaded joint breaks the bolt — which is obvious — rather than stripping the thread, which is not. Nut class 5 goes with bolts to 5.8, class 8 with 8.8, class 10 with 10.9, class 12 with 12.9, and the standard allows a higher nut class to replace a lower one but never the reverse. To reach the top classes you need more thread engaged, and a taller nut gets there at a LOWER hardness than a regular one would need — which matters, because hardness bought at the expense of ductility is how a nut cracks instead of yielding. That is what ISO 4033 is for. It shares the across-flats and the bearing face with ISO 4032; all it costs you is about 10% more height.

A thin nut is not a locknut, and the stacking order is the opposite of what most people do. ISO 898-2 is explicit that thin nuts “have a reduced loadability compared to regular nuts or high nuts, and are not designed to provide resistance to thread stripping”, and its thin-nut classes carry a leading zero — 04 and 05 — precisely to mark them as not fully loadable. At M8 their proof loads are 13,900 N and 18,300 N against a class 8 regular nut’s 31,800, so a jam nut alone carries 44% to 58% of what the joint expects. Used as a lock behind a full nut, the order matters: the THIN nut goes against the joint and the thick one on top. Matrix Engineering’s account is specific — “the thin (jam) nut nearest the joint, tightened first to 25–50% of the final torque value. The thick nut is then tightened on top to full torque while the thin nut is held against rotation” — because once assembled the OUTER nut carries the joint’s full tension and the inner one only jams the threads. Put the thin nut on the outside, which is what almost everyone does, and the thin nut is carrying the load. NASA’s own Fastener Design Manual goes further and says not to do it at all: the two-nut assembly is “too unpredictable to be reliable … It would be rare to get the correct amount of torque on each nut. A locknut is a much more practical choice than a regular nut and a jam nut.”

The bearing face is the dimension that decides whether the nut fits and whether the joint holds its preload. A nut does not press on its flats; it presses on a circle of diameter d_w, and over a clearance hole that leaves a surprisingly thin annulus — 72 mm² on an M10, about the area of a 9.6 mm circle. Push 23 kN through it and the contact pressure is over 300 MPa, which will emboss a structural steel surface, let alone an aluminium one. That embedment is preload you lose in the first few cycles. d_w is also the number to check when the question is whether the nut will foul a fillet or drop into a counterbore, because it is smaller than the spanner size and much smaller than the across-corners. Where the pressure is the problem, the washer dimensions calculator gives the area each washer series buys; where the hole and the recess are the problem, the counterbore and countersink calculator does the geometry; and the other end of the fastener is on the hex head bolt dimensions calculator. What this page deliberately does NOT do is compute thread stripping: that needs both materials and the thread form, and it has a page of its own in the bolted-joint cluster. This page gives that page its input — the engagement height you actually have.

Frequently asked questions

Related calculators

References

1. Fuller Fasteners. ISO 4032 Specifications — Hex Regular Nuts and ISO 4035 Specifications — Hex Thin Nuts. Source for the across-flats, across-corners, thickness (max and min) and bearing-face diameter dw of both families. The m_min column is the one that matters here: it is what ISO 898-2’s style definitions are written against.
2. Torqbolt. ISO 4033 Hexagon High Nuts — Dimensions, Standards, Specifications. Source for the style 2 heights. A separate fetch of the ISO 4033:2023 preview returned a table SHIFTED BY ONE ROW — it printed M27’s 46 mm across flats against M30 — which is why the figures used are Torqbolt’s and why every row was checked against the across-flats series before use.
3. Fuller Fasteners. DIN 934 Specifications — Hex Regular Nuts, cross-checked cell for cell against Andrews Fasteners’ DIN 934 Hexagon Nuts — Basic dimensions. The two agree, including the 17 mm and 19 mm across-flats at M10 and M12 and the lower heights at every size from M5 up.
4. ISO 898-2:2012 and :2022, Fasteners — Mechanical properties of fasteners made of carbon steel and alloy steel — Part 2: Nuts with specified property classes. Read from a published copy for the definitions used here, quoted: “style 0: thin nut with minimum height 0,45D ≤ m_min < 0,8D”, “style 1: regular nut with minimum height m_min ≥ 0,8D”, “style 2: high nut with minimum height m_min ≈ 0,9D”, and “thin nuts (style 0) have a reduced loadability compared to regular nuts or high nuts, and are not designed to provide resistance to thread stripping”. Its Table 2 pairs nut class 5 with bolts to 5.8, 6 to 6.8, 8 to 8.8, 9 to 9.8, 10 to 10.9 and 12 to 12.9, and notes that “nuts of a higher property class may replace nuts of a lower property class”. The proof loads quoted here are the M8 coarse row only, which is the one row this batch could read without risk of a shifted column. The standard’s scope starts at M5, which is visible in the numbers: ISO 4032 M3 and M4 sit under 0.8 D.
5. Würth Industry. Fasteners: Differences between DIN – EN – ISO standards. The single most useful document this batch read. It tabulates DIN 934 against ISO 4032 at the four changed sizes, states that “nuts according to ISO 4032, ISO 4033, ISO 4034 … may not be replaced by nuts according to DIN standards which only have got a reduced loadability according to DIN 267 Part 4 … such as DIN 934”, that “it is absolutely necessary to use at least hardness class 200 HV for high-strength screws and bolts of property class 8.8 and higher”, and that DIN 127, 128, 137, 6797, 6798 and 7980 were “withdrawn without replacement, as there is no functional guarantee in combination with high-strength screws and bolts”.
6. ISO 272:1982, Fasteners — Hexagon products — Widths across flats. The document that changed four sizes. Wikipedia’s Width across flats article cites it directly: “with ISO 272 1982 the width across flats for M10, M12, M14 and M22 were changed from 17, 19, 22 and 32 mm respectively to the current standard”. Confirmed independently by EKINSUN’s wrench-size chart (M10 17→16, M12 19→18, M14 22→21, M22 32→34) and by the DIN 934 nut tables, which still print 17 and 19.
7. Fuller Fasteners. DIN 935 Specifications — Hex Slotted and Castle Nuts. Source for the total height m, the body height m1 below the slots, the slot width and depth, and dw. Its e column carries the ISO across-flats, not the legacy DIN ones, which is worth knowing if you are pairing a castle nut with an older stud.
8. ITA Fasteners. Nylon Insert Lock Nuts — DIN, ISO Standards. Source for the DIN 985 / ISO 10511 and DIN 982 / ISO 7040 heights used here. Its across-flats column prints the LEGACY DIN figures (17 at M10, 19 at M12); Westfield Fasteners’ DIN 985 sheet notes that “DIN 985 has now been superseded by ISO 10511” while off-the-shelf parts remain to the older specification, so a nyloc nut’s spanner size has to be checked on the part and not assumed.
9. On which ISO number pairs with which DIN number: Würth’s comparison lists DIN 985 → ISO 10511; eurolab’s product page is titled DIN 985 Low Profile Nylon Insert Hexagon Lock Nuts — ISO 10511 Predominant Torque Type Hexagon Thin Nuts (Non-Metallic Insert); and Auto Lok Nut’s own note describes DIN 985 as “a thin hexagon self-locking nut with a non-metallic insert” against ISO 7040 as the normal-height form. ISO 7040 pairs with DIN 982, not with DIN 985.
10. Matrix Engineering. The Use of Two Nuts to Prevent Self Loosening. The stacking order, quoted: “the thin (jam) nut nearest the joint, tightened first to 25–50% of the final torque value. The thick nut is then tightened on top to full torque while the thin nut is held against rotation.” Wikipedia’s Jam nut article, citing the same paper and NASA RP-1228, adds that once assembled “the outer nut bears the full tension of the joint. The inner nut functions merely to add a small additional force to the outer nut and does not need to be as strong.”
11. NASA Reference Publication 1228, Fastener Design Manual, Richard T. Barrett, 1990. On helical spring (split) lock washers, quoted: “The lockwasher serves as a spring while the bolt is being tightened. However, the washer is normally flat by the time the bolt is fully torqued. At this time it is equivalent to a solid flat washer, and its locking ability is nonexistent. In summary, a lockwasher of this type is useless for locking.” On the two-nut assembly: “this type of assembly is too unpredictable to be reliable … It would be rare to get the correct amount of torque on each nut. A locknut is a much more practical choice than a regular nut and a jam nut.” The NTRS PDF could not be fetched directly here; the text was read through Engineering Library’s Fastener Design Criteria transcription of it, which names RP-1228 as its source.
12. ISO 273, Fasteners — Clearance holes for bolts and screws. Cited by number; the fine / medium / coarse columns used here are taken from EKINSUN’s What Size Clearance Hole for a Metric Bolt? ISO 273 Chart, which labels them H12, H13 and H14.