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DIN 557 · ASME B18.2.2

Square Nuts Manufacturer in India

Four flats that hold the nut still. We make square nuts to DIN 557 and ASME B18.2.2, regular and heavy, in carbon steel and stainless. Below: the nut to scale, metric and inch tables, square against hex, how a square nut locks in a slot and a finder.

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  • ISO 9001:2015 certified manufacturer
  • Metric and inch
  • Regular and heavy
  • EN 10204 3.1 / 3.2
Stainless steel square nuts with chamfered corners
DIN 557 M5 – M16 ASME 1/4 – 1-1/2 in Heavy square too
Overview

DIN 557, ASME B18.2.2 Square Nuts: Manufacturer & Exporter

A square nut is the simplest way to stop a nut turning. Drop it into a slot or against a flange and tighten the bolt from the other side: the flats do the holding, no second spanner needed.

Exotic Alloy manufactures and exports square nuts from Mumbai, India, for timber and steel construction, strut and channel systems, machinery and farm equipment builders, and fastener distributors. We supply across India and export to Kuwait, the Gulf, Africa and South-East Asia.

Metric and inch

Metric square nuts follow DIN 557, product grade C. Inch square nuts follow ASME B18.2.2 in two series, square and heavy square. Thin square nuts are on our square thin nuts page, weldable ones on square weld nuts; for six-sided nuts see hex nuts.

DIN 557 ASME B18.2.2 Heavy square UNC & UNF Stainless
Square nuts at a glance
Metric
DIN 557:1994, M5–M16, grade C
Inch
ASME B18.2.2, 1/4–1-1/2 in
Spanner
17 mm at M10 (16 on request)
Height
≈ 0.8 d (DIN); = D (heavy)
Corners
s × 1.414 across
Class
5; stainless A2, A4
Related
Thin, weld, hex nuts
DIN 557 square nut M10 to scale: 17 mm across flats, 24 mm across the corners, 8 mm high, bearing face at least 15.5 mm across DIN 557 square nut M10, to scale s 17 (spanner) e 24 across corners bearing dw ≥ 15.5 Top view m 7.42–8 s 17 Side view (chamfered corners on top) EXOTIC ALLOY
A DIN 557 M10 square nut to scale. 17 mm across flats but 24 mm across the corners: the long diagonal is what grips a slot.
Specification

Square Nut Specification

The range we manufacture and export.

StandardsDIN 557; ASME B18.2.2 square and heavy square
SizesM5–M16; 1/4–1-1/2 in
ThreadMetric coarse; UNC, UNF, 8-UN
Product gradeC (DIN 557)
Steel class5 (DIN 557); grade by agreement (inch)
StainlessA2 (304), A4 (316)
FinishPlain, zinc plated, hot-dip galvanized
Spanner optionsM10 17 or 16 mm, M12 19 or 18 mm
CertificationEN 10204 3.1; 3.2 on request
SupplyBoxed by size, or with carriage bolts
DIN 557

DIN 557 Square Nut Dimensions

Product grade C, coarse thread, mm.

SizePitch PSpanner s
max / min		Across corners e
max / min		Height m
max / min		Wrenching mw minBearing dw minkg / 1000
M50.88 / 7.6411.3 / 9.934 / 3.522.56.71.31
M6110 / 9.6414.1 / 12.535 / 4.523.28.72.77
M81.2513 / 12.5718.4 / 16.346.5 / 5.924.111.55.5
M10 (ISO width)1.516 / 15.5722.6 / 20.248 / 7.425.214.510.7
M101.517 / 16.5724 / 21.548 / 7.425.215.513
M12 (ISO width)1.7518 / 17.5725.4 / 22.8410 / 9.426.616.516.3
M121.7519 / 18.4826.9 / 24.0210 / 9.426.617.219.1
M16224 / 23.1633.9 / 30.1113 / 12.38.62238.2

DIN 557:1994, confirmed by globalfastener and fasten.it. M10 and M12 come with the DIN widths 17 and 19 mm or the ISO 272 widths 16 and 18 mm; nuts with the ISO width carry the width (SW) in their marking. mw is the height of the flats a spanner can grip, dw the diameter of the bearing face. The 1985 edition also listed M20. 2026 edition: globalfastener lists a new DIN 557:2026 with the same dimensions for M5 to M16 but without the 16 and 18 mm widths; we confirm the edition on order.

ASME inch

ASME B18.2.2 Square and Heavy Square Nuts

Inches. F across flats, H thickness.

SizeThreads
UNC / UNF		Square nut F
max / min		Square nut H
max / min		Heavy square F
max / min		Heavy square H
max / min
1/420 / 280.438 / 0.4250.235 / 0.2030.500 / 0.4880.266 / 0.218
5/1618 / 240.562 / 0.5470.283 / 0.2490.562 / 0.5460.330 / 0.280
3/816 / 240.625 / 0.6060.346 / 0.3100.688 / 0.6690.393 / 0.341
7/1614 / 200.750 / 0.7280.394 / 0.3560.750 / 0.7280.456 / 0.403
1/213 / 200.812 / 0.7880.458 / 0.4180.875 / 0.8500.520 / 0.464
5/811 / 181.000 / 0.9690.569 / 0.5251.062 / 1.0310.647 / 0.587
3/410 / 161.125 / 1.0880.680 / 0.6321.250 / 1.2120.774 / 0.710
7/89 / 141.312 / 1.2690.792 / 0.7401.438 / 1.3940.901 / 0.833
18 / 121.500 / 1.4500.903 / 0.8471.625 / 1.5751.028 / 0.956
1-1/87 / 12 / 81.688 / 1.6311.030 / 0.9701.812 / 1.7561.155 / 1.079
1-1/47 / 12 / 81.875 / 1.8121.126 / 1.0622.000 / 1.9381.282 / 1.187
1-3/86 / 12 / 82.062 / 1.9941.237 / 1.1692.188 / 2.1191.409 / 1.310
1-1/26 / 12 / 82.250 / 2.1751.348 / 1.2762.375 / 2.3001.536 / 1.433

ASME B18.2.2-2022 (same values as 2015), square nuts confirmed by AmesWeb and fasten.it, heavy square nuts by fasten.it. Across corners G max = F max × 1.414. fasten.it prints the 7/8 in heavy square H min as 0.883, more than the 0.875 basic; both ASME editions give 0.833. At 5/16 and 7/16 in the heavy square nut is no wider than the regular one, only thicker.

1/2 in square nut and heavy square nut to ASME B18.2.2, to scale: 13/16 in and 7/8 in across flats, 7/16 in and 1/2 in thick 1/2-13 to scale: ASME square nut vs heavy square nut F 13/16 in (max 0.812) H 7/16 Square nut F 7/8 in (max 0.875) H 1/2 Heavy square nut Side views across flats, ASME B18.2.2-2022. Heavy square: H = D; F = 1.5 D + 1/8 in except at 5/16 and 7/16 in. EXOTIC ALLOY
Same bolt, two nuts. The heavy square nut is as thick as the bolt diameter and 1/16 in wider at 1/2 in.
Square vs hex

Square Nut or Hex Nut: Turning Room

M10 square nut and M10 hex nut to scale with the circles their corners sweep: 24 mm for the DIN 557 square nut, 18.5 mm for the ISO 4032 hex nut M10 to scale: the circle the corners sweep when the nut turns DIN 557 square nut, s 17 corners sweep ⌀ 24.0 mm ISO 4032 hex nut, s 16 corners sweep ⌀ 18.5 mm Our calculation from s max: square s × √2, hexagon s × 2/√3 (sharp corners). Leave this room for the spanner to turn. EXOTIC ALLOY
The square nut needs a bigger circle to turn. At M10 its corners sweep 24 mm, a hex nut's 18.5 mm.
SizeSquare DIN 557
s / corners		Hex ISO 4032
s / corners		Extra swing room
M58 / 11.38 / 9.2+2.1 mm
M610 / 14.110 / 11.5+2.6 mm
M813 / 18.413 / 15.0+3.4 mm
M1017 / 24.016 / 18.5+5.6 mm
M1219 / 26.918 / 20.8+6.1 mm
M1624 / 33.924 / 27.7+6.2 mm

Our calculation from s max (sharp corners): square s × √2, hexagon s × 2/√3. Hex values for ISO 4032:2023. The same long corners that need room to turn are what lock a square nut in a slot.

Slots & channels

Square Nuts in Slots and Channels

An M10 square nut in a channel seen from above: the nut slides in when the slot is wider than 17 mm across flats and cannot turn while the slot is narrower than its corners, at least 21.54 mm Why a square nut stays put: M10 in a slot, seen from above slot 19 Slides in: slot 19 > s 17 Cannot turn: a corner hits the wall slot 19 < e min 21.54 Rule used in the finder: s max < slot < e min. Drawn to scale for DIN 557 M10 (s 17, e min 21.54). EXOTIC ALLOY
Wider than the flats, narrower than the corners. Then the nut slides in and cannot turn.
  • Slot ≤ s max: the nut may not slide in.
  • s max < slot < e min: slides in, cannot turn.
  • Slot ≥ e min: it may turn, depending on how far its corners are chamfered.
  • Against a flange or a second plate, one flat is enough to hold the nut.
  • The finder below checks your slot for any size.
Finder

Square Nut Finder: Dimensions & Slot Fit

Pick the nut and enter your slot; get the dimensions, whether it locks, and the order line.

Nut & slot

Dimensions from the tables on this page; inch sizes converted at 25.4 mm. Slot check: s max < slot < e min means it slides in and cannot turn. Leave the slot empty to skip it. Mass for steel DIN 557 nuts.

Result
17
mm across flats
8
mm high (max)
Across corners:21.54–24 mm
Slot check:19 mm: slides in, cannot turn
Thread:M10 × 1.5, hole 11 mm (ISO 273)
Mass:≈ 13 kg
Designation:1000 pcs square nut DIN 557 – M10 – 5

Materials

Square Nut Materials & Finishes

MaterialClass / gradeFinishWhere
Carbon steel5 (DIN 557)Plain, zinc platedMachinery, channel systems, indoor
Carbon steelAs ordered (inch)Hot-dip galvanizedTimber and outdoor construction
Stainless A2 (304)A2PlainFood, water and general outdoor use; as in the photo
Stainless A4 (316)A4PlainCoastal, marine and chemical areas

DIN 557 names steel property class 5; ASME B18.2.2 leaves the grade to the order (its 2015 and 2022 tables reference SAE J995 for steel and ASTM F594 / F467 for stainless and non-ferrous nuts). Match the nut to the bolt and the bolt coating.

Carbon steel
Class 5

Plain, zinc or galvanized.

10101035
Stainless
A2 · A4

As in the photo.

304316
Brass
On request

Electrical and decorative.

Brass
Manufacturing

How Our Square Nuts Are Made

1

Wire / bar

Steel or stainless, certified by heat.

2

Form

Square blank cold or hot formed, hole pierced.

3

Chamfer

Corners chamfered, as in the photo.

4

Tap

Metric, UNC or UNF thread.

5

Finish

Zinc, galvanized or passivated.

6

Inspect

Thread, flats and height checked.

Applications

Where Our Square Nuts Are Used

Timber construction

With carriage bolts in beams and decks.

Slots & channels

Held in a slot while the bolt is tightened.

Farm machinery

Implements, frames and guards.

Machinery

Fixtures and blind locations.

Furniture

Frames and knock-down fittings.

Electrical

Terminal blocks and panel fixings.

Quality & testing

Square Nut Inspection & Certification

CheckMethodApplied to
ThreadGO / NOT GO plug gaugesEvery lot
s, e, mCalipers, micrometerEvery lot
Proof loadISO 898-2 (class 5), ISO 3506-2 (stainless)Every lot
HardnessRockwell or VickersSteel lots
CoatingThickness gaugeCoated lots
MaterialHeat certificate, PMI on requestEvery heat

Every shipment includes

  • EN 10204 3.1 certificate
  • Lot number on every box
  • Packing list by size

On request

  • EN 10204 3.2 with third-party inspection
  • Salt spray tests on coated nuts
  • Sets with carriage bolts and washers
FAQ

Square Nut Questions, Answered

A nut with four flat sides instead of six. Its long flats and corners hold it against a slot, channel or neighbouring surface, so it cannot turn while the bolt is tightened. Metric square nuts are made to DIN 557 (M5 to M16), inch square and heavy square nuts to ASME B18.2.2 (1/4 to 1-1/2 in).

17 mm across flats (16 mm on request, the ISO 272 width), 8 mm high, at most 24 mm across the corners and a bearing face at least 15.5 mm across. 1000 steel nuts weigh about 13 kg.

Steel property class 5, product grade C. We also make them in stainless steel A2, as in the photo, and A4.

In ASME B18.2.2 the heavy square nut is thicker at every size, as thick as the bolt diameter (1/2 in for a 1/2 in bolt against 7/16 in), and wider at most sizes. At 5/16 and 7/16 in both nuts have the same width across flats.

Its corners sweep a circle of the width across flats times 1.414. At M10 that is 24 mm for a DIN 557 square nut against 18.5 mm for an ISO 4032 hex nut, so leave more room around a square nut for the spanner.

Yes, if the slot is wider than the nut across flats and narrower than its corners. An M10 DIN 557 nut (17 mm across flats, at least 21.54 mm across corners) slides into a 19 mm slot and cannot turn in it. The finder below checks any slot.

Yes. ASME B18.2.2 lists UNC and UNF threads for every size from 1/4 to 1-1/2 in, and 8-UN from 1-1/8 in.

DIN has revised DIN 557; globalfastener lists a 2026 edition with the same main dimensions for M5 to M16, without the 16 and 18 mm widths for M10 and M12. Our tables follow the 1994 edition, which two sources confirm.
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