Carriage Bolts Manufacturer in India | DIN 603 Mushroom Head Bolts

Overview

DIN 603 Mushroom Head Bolts & ASME B18.5 Carriage Bolts: Manufacturer & Stockist

A carriage bolt has a smooth domed head and a square neck under it. Driven through a snug hole, the neck locks into the wood or a square hole in steel, so the nut can be tightened from one side without holding the head. The head leaves nothing to grip, so the joint is also hard to undo from the outside.

Exotic Alloy manufactures carriage bolts in Mumbai, India. Metric mushroom head bolts follow DIN 603, and inch round head square neck bolts follow ASME B18.5. Heads and necks are cold forged in one blow, and threads are rolled. We stock and supply timber builders, playground, fencing, trailer and agricultural equipment makers across India, and export to the UK, Europe, the Gulf and Africa.

Ready Stock, Custom Lengths

Common DIN 603 M6 to M12 and inch ¼″ to ½″ carriage bolts in zinc plated, hot-dip galvanized and A2 stainless ship from stock. Long lengths, A4 and Grade 8 bolts, and ribbed or short-neck styles are made to order.

M5 – M20 | ¼ – ¾″ Square, short, ribbed, fin neck 4.6, 8.8, Grade 5 / 8 HDG, A2, A4 Bolt, nut & washer kits

Carriage bolt at a glance

Head: Smooth dome, about 2.4 × d across (DIN 603)
Neck: Square, about d wide; locks in wood or a square hole
Length: Measured from under the head, neck included
Standards: DIN 603 (metric), ASME B18.5 (inch)
Grades: 4.6, 8.8; low carbon, Grade 5, Grade 8; A2, A4
Related: Elevator bolts, lag bolts, square head bolts

DIN 603 M10 × 60, drawn to scale (view from below at 80 %). The dome is 24 mm across but only 5 mm high, and the square neck is 10 mm wide and 6 mm deep. The length l runs from under the head, so it includes the neck.

Specification

Carriage Bolt Specification

The range we manufacture and supply.

StandardsDIN 603 (05/2017) cup head square neck bolts, product grade C; ASME B18.5 round head square neck, short neck, ribbed neck and fin neck bolts; ISO 8678 short-neck bolts on request

Size rangeM5 to M20 in lengths 16 to 300 mm; ¼″ to ¾″ in lengths ½″ to 20″; longer to order

ThreadMetric coarse 6g; UNC 2A; DIN 603 thread lengths by length range; inch minimum 2D + ¼″ (L ≤ 6″) or 2D + ½″ (L > 6″); full thread on short bolts

Head & neckSmooth dome (mushroom) head; square, short square, ribbed or fin neck

GradesISO 898-1 classes 4.6 and 8.8; SAE J429 low carbon, Grade 5, Grade 8; ISO 3506 A2-70 and A4-70; 18-8 stainless (inch)

MaterialsLow and medium carbon steel; alloy steel for Grade 8; stainless 304 / 316; silicon bronze to order

FinishPlain; zinc plated clear or yellow; hot-dip galvanized (ISO 10684 / ASTM F2329); passivated stainless; black

MarkingProperty class or grade lines on the head for 8.8, Grade 5 and Grade 8; A2 / A4 on stainless; smooth unmarked heads on request

CertificationMill certificate; EN 10204 3.1 with dimensions, hardness and coating thickness; PMI for stainless

PackingBoxes, bulk cartons or retail packs; bolt, nut and washer kits on request

Types

Types of Carriage Bolts We Manufacture

The neck decides what the bolt locks into.

Five neck styles (schematic). The standard square neck suits wood and square-punched steel. The short neck suits thin sheet. Ribs bite into round holes in soft metal, and fins grip wood. The flat-head version sits flush; see also elevator bolts.

DIN 603 Mushroom Head Bolts

M5 – M20 · 4.6 / 8.8 / A2 / A4

The European carriage (coach) bolt for timber, fencing, playgrounds and steel channels, with a large, low dome.

ASME B18.5 Carriage Bolts

¼ – ¾″ · low carbon / Gr 5 / Gr 8 / 18-8

Round head square neck bolts in UNC, for decks, trailers, farm machinery and wooden structures.

Hot-Dip Galvanized Carriage Bolts

ISO 10684 / ASTM F2329

For treated timber and outdoor structures, supplied with over-tapped galvanized nuts.

Stainless Carriage Bolts

A2 (304) · A4 (316)

For coastal decks, docks, pools and food plants, as in the product photo.

Carriage bolt or hex bolt?

Feature	Carriage bolt	Hex bolt
Head	Smooth dome, nothing to grip	Hexagon for a spanner
Stopping rotation	Square neck locks in the hole	Spanner on the head
Tools needed	One spanner, on the nut	Two spanners
Security	Hard to remove from the head side	Easy to remove
Best in	Timber, square-punched steel	Steel structures and machinery

Dimensions

Carriage Bolt Dimensions: DIN 603 & ASME B18.5

Thread d	Pitch P	Head d_k nom, mm	Head height k min / max	Square depth f min / max	Square width v min / max	Thread length b l ≤ 125 / ≤ 200 / > 200
M5	0.8	13	2.7 / 3.3	2.9 / 4.1	4.52 / 5.48	16 / 22 / –
M6	1	16	3.12 / 3.88	3.4 / 4.6	5.52 / 6.48	18 / 24 / –
M8	1.25	20	4.12 / 4.88	4.4 / 5.6	7.42 / 8.58	22 / 28 / 41
M10	1.5	24	4.62 / 5.38	5.4 / 6.6	9.42 / 10.58	26 / 32 / 45
M12	1.75	30	6.05 / 6.95	7.25 / 8.75	11.3 / 12.7	30 / 36 / 49
M16	2	38	8.05 / 8.95	11.1 / 12.9	15.3 / 16.7	38 / 44 / 57
M20	2.5	46	9.95 / 11.05	14.1 / 15.9	19.16 / 20.84	46 / 52 / 65

DIN 603 (05/2017, same values as the 2010 edition), product grade C, dimensions in mm. The head diameter d_k is nominal; for example, the M10 maximum is 24.65 mm.

Size	Threads / in	Body E max / min	Head A max / min	Head H max / min	Square O max / min	Square depth P max / min	Min. thread L ≤ 6″ / > 6″
1/4″	20	0.2500 / 0.237	0.594 / 0.563	0.145 / 0.125	0.260 / 0.245	0.156 / 0.125	0.750 / 1.000
5/16″	18	0.3125 / 0.298	0.719 / 0.688	0.176 / 0.156	0.324 / 0.307	0.187 / 0.156	0.875 / 1.125
3/8″	16	0.3750 / 0.360	0.844 / 0.782	0.208 / 0.188	0.388 / 0.368	0.219 / 0.188	1.000 / 1.250
1/2″	13	0.5000 / 0.483	1.094 / 1.032	0.270 / 0.250	0.515 / 0.492	0.281 / 0.250	1.250 / 1.500
5/8″	11	0.6250 / 0.605	1.344 / 1.219	0.344 / 0.313	0.642 / 0.616	0.344 / 0.313	1.500 / 1.750
3/4″	10	0.7500 / 0.729	1.594 / 1.469	0.406 / 0.375	0.768 / 0.741	0.406 / 0.375	1.750 / 2.000

ASME B18.5 round head square neck bolts, dimensions in inches. Length is measured from the underside of the head to the end of the bolt.

Nominal size	To 1″	Over 1 to 2½″	Over 2½ to 4″	Over 4 to 6″	Over 6″
No. 8 to ⅜″	+0.02 / −0.03	+0.02 / −0.04	+0.04 / −0.06	+0.06 / −0.10	+0.10 / −0.18
7/16 and ½″	+0.02 / −0.03	+0.04 / −0.05	+0.06 / −0.08	+0.08 / −0.10	+0.12 / −0.18
9/16 to ¾″	+0.02 / −0.03	+0.06 / −0.08	+0.08 / −0.10	+0.10 / −0.10	+0.14 / −0.18

Length tolerance in inches for ASME B18.5 round head square neck bolts, by nominal length.

Installation

Installing Carriage Bolts in Wood & Steel

Two ways the neck locks (not to scale). In timber, drill a hole the bolt's size and let the nut pull the square neck into the wood. In steel, the neck needs a square hole. A round hole in steel will not stop the bolt turning; use a ribbed-neck bolt or hold the head.

Do

Drill the hole to the bolt diameter so the neck has wood to grip
Tap the bolt through until the head sits down
Use a large or round plate washer under the nut on timber
Re-tighten timber joints after the wood has dried and shrunk

Don't

Oversize the hole in wood: the neck will spin
Over-tighten: the dome sinks and crushes the fibres
Use bright zinc plated bolts in treated or outdoor timber
Use a standard square neck in a round hole in steel

Length calculator

Carriage Bolt Length Calculator

Enter the thickness of the parts being joined. We add the washer, nut and two threads of projection, round up to a standard length, and check that the thread reaches into the joint.

Your joint

Standard

Size

Joint thickness, mm

Washer: ISO 7089 or USS flat. Nut: ISO 4032 or ASME B18.2.2 hex nut. Standard lengths: the metric R-series to 300 mm; inch lengths in ¼″ steps to 3″, then ½″ steps.

Suggested bolt

M10 × 55

standard length

Length needed:53.4 mm

Thread length:26 mm

Thread starts from head:29 mm

Grades & finishes

Carriage Bolt Grades & Finishes

Grade	Standard	Proof	Yield min	Tensile min	Hardness
Low carbon (inch)	ASME B18.5 bolts, SAE J429 Grade 1 level	33 ksi	36 ksi	60 ksi	B70–B100
Grade 5	SAE J429	85 ksi	92 ksi	120 ksi	C25–C34
Grade 8	SAE J429	120 ksi	130 ksi	150 ksi	C33–C39
18-8 stainless (inch)	ASTM F593 type	–	65 ksi	100–150 ksi	B95–C32
Class 4.6	ISO 898-1	225 MPa	240 MPa	400 MPa	120–220 HV
Class 8.8	ISO 898-1	580 / 600 MPa	640 / 660 MPa	800 / 830 MPa	22–32 / 23–34 HRC
A2-70 / A4-70	ISO 3506-1	–	450 MPa	700 MPa	–

8.8 values: first figure up to M16, second above M16.

Finish	Specification	Use
Zinc plated	ISO 4042 / ASTM F1941	Indoor, dry timber and furniture
Hot-dip galvanized	ISO 10684 / ASTM F2329	Fences, decks, treated timber, playgrounds
Black / plain	Oiled	Painted steelwork, dry interiors
Passivated stainless	ASTM A967 / A380	A2 and A4 carriage bolts

Materials

Carriage Bolt Materials

Every grade links to its datasheet on this site.

Low carbon steel

4.6 · low carbon

Ductile cold-heading steels for the dome and square neck.

1010 1018

Medium carbon / boron

8.8 · Grade 5

Quenched and tempered for higher strength.

1035 15B35H

Stainless A2

304

Outdoor timber, furniture and fencing.

304

Stainless A4

316

Marine, pool and chemical environments.

316 316L

Manufacturing

How Our Carriage Bolts Are Made

1

Wire

Annealed carbon, boron or stainless wire, received by heat with mill certificates.

2

Heading

Multi-station cold heading forms the dome and square neck, with crisp corners that grip.

3

Thread rolling

Metric 6g or UNC 2A threads rolled to the DIN 603 or B18.5 thread length.

4

Heat treatment

8.8, Grade 5 and Grade 8 bolts quenched and tempered.

5

Finishing

Zinc plating, hot-dip galvanizing with spinning, or stainless passivation.

6

Inspection

Head, neck and thread gauged; hardness and coating checked per lot.

Applications

Where Our Carriage Bolts Are Used

Decks, pergolas & timber frames

Through-bolting beams, posts and joists with a smooth head on the visible side.

Playgrounds & street furniture

Smooth, tamper-resistant heads on swings, benches and play equipment.

Fencing & gates

Rails, posts and gate hardware, galvanized or stainless.

Trailers & truck bodies

Fixing timber floors and sides to steel frames with square-punched holes.

Farm machinery

Grade 5 and 8 carriage bolts on implements, guards and shields.

Racking & steel channels

Bolting to slotted angle and strut with square holes.

Quality & testing

Carriage Bolt Inspection & Certification

Check	Method	Applied to
Head diameter & height	Callipers against d_k / k or A / H	Every lot
Square neck	Width v / O and depth f / P	Every lot
Thread	Ring gauges, after coating	Every lot
Hardness	Rockwell	Every heat-treatment lot
Tensile / proof	ISO 898-1 / ASTM F606	8.8, Grade 5 and Grade 8
Coating	Magnetic thickness gauge	Galvanized and plated lots

Every shipment includes

Mill certificate with heat number
Dimensional and hardness report
Coating thickness report

On request

EN 10204 3.1 certificate
Proof load and tensile test report
Salt spray test

FAQ

Carriage Bolt Questions, Answered

A carriage bolt, also called a coach bolt or mushroom head bolt, has a smooth domed head with a square neck under it. The square neck locks into the wood or into a square hole in steel, so the bolt cannot turn while the nut is tightened from the other side. The smooth head leaves nothing to grip, which also makes the joint tamper resistant. Metric carriage bolts are made to DIN 603 and inch ones to ASME B18.5.

Carriage bolt length is measured from the underside of the head to the end of the bolt, so the square neck is included in the length but the domed head is not. Specify the thread size and this length, for example M10 x 60 or 3/8-16 x 3 inch.

A DIN 603 M10 carriage bolt has a nominal head diameter of 24 mm, a head height of 4.62 to 5.38 mm, a square neck 9.42 to 10.58 mm wide and 5.4 to 6.6 mm deep, and a thread length of 26 mm for lengths up to 125 mm. The full DIN 603 table from M5 to M20 is on this page.

Add the thickness of the parts being joined, the washer, the nut and about two threads of projection, then round up to the next standard length. For two 20 mm timbers with an M10 bolt that is 40 + 2 + 8.4 + 3 = 53.4 mm, so an M10 x 55 bolt. Check that the thread starts inside the joint so the nut can tighten; the calculator on this page does both checks.

Drill a hole the same diameter as the bolt, tap the bolt through until the head is down, then fit a washer and nut on the far side. As the nut is tightened, the square neck is pulled into the wood and stops the bolt turning. Use a large washer on soft timber so the nut does not sink in, and do not over-tighten, which crushes the wood fibres under the head.

Yes, if the steel has a square hole that fits the neck, as on steel channels, trailer frames and some agricultural equipment. In a round hole in steel the neck cannot grip, so the bolt will spin unless the head is held. For high-strength steel joints use Grade 5, Grade 8 or class 8.8 carriage bolts.

Inch carriage bolts are commonly low-carbon steel (proof 33,000 psi, tensile 60,000 psi minimum), SAE J429 Grade 5 (120,000 psi) or Grade 8 (150,000 psi), and 18-8 stainless. Metric DIN 603 carriage bolts are commonly property class 4.6 or 8.8, or A2 and A4 stainless steel.

Use hot-dip galvanized or stainless steel carriage bolts. Electroplated zinc is too thin for outdoor timber and is attacked by copper-based wood preservatives. Stainless A4 (316) is the best choice near the sea, on pools and docks, and for long-life structures.