Square Head Bolts Manufacturer in India | DIN 478 Square Head Screws

Overview

DIN 478 Square Head Screws & ASME Square Bolts: Manufacturer & Supplier

Square head bolts are the oldest bolt form and still the right choice for many jobs. They take a spanner on four broad flats, sit still in timber while the nut is turned, and in the DIN versions make compact, robust clamping and adjusting screws.

Exotic Alloy manufactures square head bolts in Mumbai, India, for machine and fixture builders, rail and timber construction, agricultural equipment and maintenance. We supply across India and to Egypt, the Gulf, Africa and Europe. Heads are hot or cold forged, corners are turned on DIN heads, and threads are rolled.

Two quite different families

Metric DIN square heads are narrow and tall: an M12 head is 13 mm across flats, against 18 mm for an ISO 4014 hex bolt. Inch ASME square bolts are broad and low, about 1.5 × the diameter across flats. Choose by the job, not just the thread.

DIN 478 / 479 / 480 M5 – M24 ASME ¼ – 1½″ Steel & stainless Square nuts to match

Square head bolt at a glance

DIN head: s ≈ d, tall; corners turned
ASME head: F ≈ 1.5 D, low
Tools: Open-end spanner, 8-point socket
Length: From under the head or collar
Standards: DIN 478, 479, 480; ASME B18.2.1
Related: Machine bolts, carriage bolts, hex bolts

DIN 478 M12 × 50, drawn to scale (end view at 117 %). The square is 13 mm across flats, and its corners are turned to a 17 mm circle, so the head is not a sharp square. The collar gives a round, flat bearing face larger than the head.

Specification

Square Head Bolt Specification

The range we manufacture and supply.

StandardsDIN 478 (with collar), DIN 479 (short dog point, 2016), DIN 480 (collar and oval half dog point), all product grade A; ASME B18.2.1 square bolts

Size rangeDIN 478 / 479 M5 to M24; DIN 480 M8 to M24; ASME ¼″ to 1½″; lengths to order

ThreadMetric coarse 6g, fine pitch to order; UNC 2A; DIN 478 thread length b by length range

GradesProperty classes 5.6 and 8.8; A2 / A4 stainless; ASTM A307 Grade A, SAE J429 Grade 5, ASTM F593 (inch)

MaterialsLow and medium carbon steel, alloy steel, stainless 304 / 316, brass and silicon bronze to order

FinishPlain; zinc plated; hot-dip galvanized; black; passivated stainless

HeadDIN: corners turned to diameter e; ASME: full square, plain bearing face

Supplied withSquare nuts (ASME B18.2.2), hex nuts, square or flat washers, lock nuts for DIN 479

CertificationMill certificate; EN 10204 3.1; PMI for stainless

PackingBoxes, bulk cartons, bolt and nut kits

Types

Types of Square Head Bolts We Manufacture

Four square head bolts, drawn to the same scale from the standard tables (DIN 480 schematic). The narrow, tall DIN heads and the broad, low ASME head are made for different jobs.

DIN 478 Square Head Bolts with Collar

M5 – M24 · product grade A

The collar gives a large round bearing face. Used as clamping screws in fixtures, jigs and machine frames.

DIN 479 Dog Point Screws

M5 – M24 · DIN 479:2016

A short dog point locates in a hole or groove. Used as adjusting, stop and pressure screws with a lock nut.

DIN 480 Collar & Oval Point

M8 – M24

Collar plus an oval half dog point with a rounded end, for pressure screws that swivel on the part.

ASME B18.2.1 Square Bolts

¼ – 1½″ · A307 · galvanized

Broad heads for timber, rail, docks and heritage machinery, with square nuts. See also machine bolts.

Dimensions

Square Head Bolt Dimensions: DIN 478, DIN 479 & ASME B18.2.1

Size	Pitch P	s across flats	e max across corners	k head height	d_c max collar dia.	c collar	b l ≤ 125 / > 125
M5	0.8	5	6.5	7	9.5	2	16 / –
M6	1	6	8	8	10.5	2	18 / –
M8	1.25	8	10	10	13.5	2	22 / –
M10	1.5	10	13	13	16.5	3	26 / 32
M12	1.75	13	17	15	19.5	3	30 / 36
M16	2	16 / 17	21 / 22	20	25	4	38 / 44
M20	2.5	21 / 22	27 / 28	25	31	5	46 / 52
M24	3	24	32	28	36	6	54 / 60

DIN 478:1985, nominal values in mm. For M16 and M20 the standard allows two head widths (16 / 17 and 21 / 22 mm); state the width when ordering.

Size	Pitch P	s across flats	e max across corners	k head height	d_p max dog point dia.	z₁ min dog point length	ISO 4014 hex s same thread
M5	0.8	5	6.5	5	3.5	1.25	8
M6	1	6	8	6	4	1.5	10
M8	1.25	8	10	8	5.5	2	13
M10	1.5	10	13	10	7	2.5	16
M12	1.75	13	17	12	8.5	3	18
M16	2	16 / 17	21 / 22	16	12	4	24
M20	2.5	21 / 22	27 / 28	20	15	5	30
M24	3	24	32	22	18	6	36

DIN 479:2016 (same values as the 1985 edition), mm. The last column shows the ISO 4014 hex head width for the same thread, for comparison.

Size	Threads / in	F across flats max / min	G across corners max / min	H head height max / min	E body dia. max / min
1/4″	20	0.375 / 0.362	0.530 / 0.498	0.188 / 0.156	0.260 / 0.237
5/16″	18	0.500 / 0.484	0.707 / 0.665	0.220 / 0.186	0.324 / 0.298
3/8″	16	0.562 / 0.544	0.795 / 0.747	0.268 / 0.232	0.388 / 0.360
7/16″	14	0.625 / 0.603	0.884 / 0.828	0.316 / 0.278	0.452 / 0.421
1/2″	13	0.750 / 0.725	1.061 / 0.995	0.348 / 0.308	0.515 / 0.482
5/8″	11	0.938 / 0.906	1.326 / 1.244	0.444 / 0.400	0.642 / 0.605
3/4″	10	1.125 / 1.088	1.591 / 1.494	0.524 / 0.476	0.768 / 0.729
7/8″	9	1.312 / 1.269	1.856 / 1.742	0.620 / 0.568	0.895 / 0.852
1″	8	1.500 / 1.450	2.121 / 1.991	0.684 / 0.628	1.022 / 0.976
1-1/8″	7	1.688 / 1.631	2.386 / 2.239	0.780 / 0.720	1.149 / 1.098
1-1/4″	7	1.875 / 1.812	2.652 / 2.489	0.876 / 0.812	1.277 / 1.223
1-3/8″	6	2.062 / 1.994	2.917 / 2.738	0.940 / 0.872	1.404 / 1.345
1-1/2″	6	2.250 / 2.175	3.182 / 2.986	1.036 / 0.964	1.531 / 1.470

ASME B18.2.1 square bolts, inches. Length is measured under the head; thread length is 2D + ¼″ up to 6″ long and 2D + ½″ above.

Square vs hex

Square Head vs Hex Head: Bearing Area & Clearance

½″ square and hex heads, same 0.750″ width across flats, to scale. The red circle is the swing diameter the corners need. Bearing areas are the head outline minus a 17/32″ hole (our calculation).

Size	Square F max, in	Hex F basic, in	Square G max swing dia.	Hex G sharp corners	Square bearing area in²	Hex bearing area in²	Square vs hex
1/4″	0.375	0.438	0.530	0.505	0.078	0.104	−24 %
5/16″	0.500	0.500	0.707	0.577	0.157	0.124	+27 %
3/8″	0.562	0.562	0.795	0.650	0.186	0.144	+29 %
7/16″	0.625	0.625	0.884	0.722	0.218	0.166	+32 %
1/2″	0.750	0.750	1.061	0.866	0.341	0.265	+28 %
5/8″	0.938	0.938	1.326	1.083	0.542	0.423	+28 %
3/4″	1.125	1.125	1.591	1.299	0.786	0.617	+27 %
7/8″	1.312	1.312	1.856	1.516	1.076	0.847	+27 %
1″	1.500	1.500	2.121	1.732	1.415	1.113	+27 %
1-1/8″	1.688	1.688	2.386	1.949	1.799	1.416	+27 %
1-1/4″	1.875	1.875	2.652	2.165	2.226	1.755	+27 %
1-3/8″	2.062	2.062	2.917	2.382	2.699	2.131	+27 %
1-1/2″	2.250	2.250	3.182	2.598	3.221	2.543	+27 %

Our calculation from ASME B18.2.1 square bolt and hex bolt widths, with a D + 1/32″ clearance hole. From 5/16″ up both heads are the same width across flats, so the square gains 27 to 32 % bearing area. At ¼″ the square head is narrower (3/8″ vs 7/16″) and has less.

Uses

How Square Head Bolts Are Used

Three typical joints (sections, schematic). DIN 478 and 479 screws go into tapped holes; the DIN 479 head is about as wide as a clearance hole, so it is not a through-bolt. The ASME square bolt passes through and takes a square nut.

Do

Use an 8-point socket or a well-fitting open-end spanner
Leave room for the corners to swing: half the diameter across corners from the axis
Lock adjusting screws (DIN 479 / 480) with a lock nut
Fit square washers under heads and nuts on timber

Don't

Force a 6- or 12-point socket onto a square head
Use a DIN 479 screw through a clearance hole: the head can pull through
Mix up M16 / M20 head widths: they come in two sizes
Use plain steel square bolts in treated or outdoor timber: galvanize them

Spanner finder

Square Head Spanner, Clearance & Bearing Finder

Choose the bolt to get the spanner and socket, the room its corners need to turn, and its bearing area compared with a hex bolt. Add a clamp load to see the pressure under the head.

Your bolt

Standard

Size

Clamp load, kN

Bearing area = head (or DIN 478 collar) minus the clearance hole: ISO 273 medium for metric, D + 1/32″ for inch. The hex comparison uses ISO 4014 or ASME B18.2.1 hex bolts of the same thread.

Result

13

mm spanner

8.5

mm axis to wall

Swing diameter (corners):17 mm

Head height:15 mm

Bearing area:155.5 mm²

Hex bolt, same thread:18 mm, 137.5 mm²

Pressure under head:–

Grades & materials

Square Head Bolt Grades & Materials

Grade	Standard	Tensile min	Yield min	Typical use
5.6	ISO 898-1	500 MPa	300 MPa	General DIN 478 / 479 screws
8.8	ISO 898-1	800 / 830 MPa	640 / 660 MPa	Heavier clamping and pressure screws
A2-70 / A4-70	ISO 3506-1	700 MPa	450 MPa	Food, marine and outdoor equipment
A307 Grade A	ASTM A307	60 ksi	—	Standard inch square bolts, timber
Grade 5	SAE J429	120 ksi	92 ksi	Higher-strength inch square bolts
F593 Group 1 / 2	ASTM F593	per F593 condition		304 / 316 stainless inch bolts

8.8: first value up to M16, second above M16. SAE Grade 5 values up to 1″.

Carbon steel

5.6 · A307

Forging and cold-heading steels for standard square heads.

1018 1022

Medium carbon / alloy

8.8 · Grade 5

Quenched and tempered for higher clamp loads.

1035 4140

Stainless

A2 · A4

Corrosion resistant square heads for food and marine equipment.

304 316

Non-ferrous

To order

Brass and bronze square heads for marine timber and restoration.

All materials

Manufacturing

How Our Square Head Bolts Are Made

1

Bar & wire

Certified carbon, alloy or stainless stock, cut to length.

2

Forging

Square head and collar cold or hot forged; large sizes hot forged.

3

Turning

DIN head corners turned to e; dog points and oval points turned.

4

Thread rolling

Metric or UNC threads rolled to length b.

5

Heat treatment

8.8 and Grade 5 quenched and tempered.

6

Finishing

Zinc plating, hot-dip galvanizing or passivation, then inspection.

Applications

Where Our Square Head Bolts Are Used

Jigs & fixtures

DIN 478 clamping screws and DIN 479 locating screws.

Machine adjustment

Jacking, levelling and stop screws with lock nuts.

Rail & track

Square head bolts in timber sleepers and track fittings.

Timber construction

Galvanized square bolts and nuts in docks, bridges and barns.

Agricultural equipment

Square heads on implements, harrows and conveyors.

Restoration

Period-correct square heads for heritage machinery and buildings.

Quality & testing

Square Head Bolt Inspection & Certification

Check	Method	Applied to
Width across flats	Snap gauge / callipers, s or F	Every lot
Across corners & height	Callipers, e / G and k / H	Every lot
Collar & dog point	Callipers, d_c, d_p, z	Every lot
Thread	Ring gauges	Every lot
Hardness / tensile	ISO 898-1, ASTM F606	Heat-treated and graded lots
Coating	Magnetic thickness gauge	Plated and galvanized lots

Every shipment includes

Mill certificate with heat number
Dimensional report
Lot number on every box

On request

EN 10204 3.1 certificate
Tensile and hardness reports
PMI for stainless

FAQ

Square Head Bolt Questions, Answered

A square head bolt has a four-sided head instead of a hexagon. Metric square head bolts to DIN 478, 479 and 480 have small, tall heads about as wide as the thread and are used as clamping, adjusting and pressure screws. Inch square bolts to ASME B18.2.1 have broad, low heads about 1.5 times the thread diameter across flats and are used as through-bolts in timber and steel.

All three are product grade A square head bolts. DIN 478 has a round collar under the square head, M5 to M24. DIN 479 has no collar but a short dog point at the end of the thread, M5 to M24. DIN 480 has both a collar and an oval half dog point with a rounded end, M8 to M24.

The spanner size equals the width across flats s: 8 mm for M8, 10 mm for M10 and 13 mm for M12. For M16 and M20 the standard allows two widths, 16 or 17 mm and 21 or 22 mm, so check the head or order the width you need. Use an open-end spanner, an adjustable spanner or an 8-point socket.

A square head bites into timber and does not turn while the nut is tightened, and an inch square bolt from 5/16 inch up has about 27 to 32 percent more bearing area than a hex bolt of the same size. Metric DIN square heads are narrow and tall, so they fit tight spaces and take a large spanner contact area. Square heads are also used to match existing and heritage equipment.

Use an 8-point (double square) socket or a 4-point socket of the head's width across flats. Ordinary 6-point and 12-point sockets do not fit a square head. Open-end and adjustable spanners also work, but need a 90 degree turn between grips, or 45 degrees if the spanner is flipped.

The short dog point is a plain, smaller-diameter end on the thread. It enters a hole or groove to locate a part, presses on a surface without damaging the thread, and guides the screw. DIN 479 screws are tightened into a tapped hole, often with a lock nut, as adjusting, stop or pressure screws.

An inch square bolt is about 1.5 times its diameter across flats: a 1/2 inch bolt is 0.750 inch across flats, 1.061 inch across corners and 0.308 to 0.348 inch high. The 1/4 inch size is 3/8 inch across flats. ASME B18.2.1 standardizes square bolts from 1/4 to 1-1/2 inch.

Metric square head bolts are made in property classes such as 5.6 and 8.8 and in A2 and A4 stainless steel. Inch square bolts are usually ASTM A307 Grade A, with SAE J429 Grade 5 and ASTM F593 stainless to order. Finishes are plain, zinc plated, hot-dip galvanized for timber and outdoor work, or passivated stainless.