MF FASTENER INDUSTRIES LLC Manufacturer of anchor bolts, studs & plate washers · Importer & stockist of fasteners

Technical datasheet DIN 603 — Cup head square neck bolt (carriage bolt)

Reference only — for design, verification or contractual purposes refer to the current issue of the original standard. MF Fastener Industries LLC · sales@mfindllc.com · +971 6 767 2469 · mfindllc.com

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Dimensional datasheet

DIN 603 carriage bolt

Round cup head with a square neck under it. The square locks into a matching square hole or bites into timber, so the bolt is tightened from the nut alone. Also called a coach bolt or round head square neck bolt.

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d nominal thread diameterdk head diameterk head heightl length under head

Dimensions

millimetres

Metric coarse thread. The square neck measures the same across flats as the nominal diameter — an M12 bolt has a 12 mm square neck.

Size	Pitch	dk — head dia	k — head height	Square neck	Standard lengths
M6	1.00	16.0	3.5	6.0 mm	16 – 100
M8	1.25	20.0	4.5	8.0 mm	20 – 140
M10	1.50	24.0	5.5	10.0 mm	25 – 180
M12	1.75	30.0	7.0	12.0 mm	30 – 200
M16	2.00	38.0	9.0	16.0 mm	40 – 240
M20	2.50	46.0	11.0	20.0 mm	50 – 260

The square neck must be held by something

In steel the hole is punched or drilled square, or the neck sits in a slot. In timber the square is pulled into the wood as the nut is tightened.

In a plain round hole in steel the bolt simply spins. If your hole is round, use a hex bolt instead.

The head cannot be gripped

There is no drive on a cup head. Once the square is seated, all tightening is from the nut side, and the bolt cannot be undone from the head.

That is the point of it — carriage bolts are used where the head side is not accessible, or where a smooth tamper-resistant face is wanted.

Property classes

ISO 898-1

Class	Tensile min	Yield min	Typical use
4.6	400 N/mm²	240 N/mm²	Timber and general
4.8	400 N/mm²	340 N/mm²	Common commercial grade
8.8	800 N/mm²	640 N/mm²	Structural timber connections
A2-70 / A4-80	700 / 800 N/mm²	450 / 600 N/mm²	Stainless, external

Most commercial carriage bolts are class 4.6 or 4.8. Where the connection is structural, specify 8.8 and ask for the certificate.

Related forms

—

Standard	Head	Neck	Use
DIN 603	Cup, domed	Square	Timber, punched steel
DIN 605	Cup, domed	Square, long	Thicker material
DIN 607	Cup, domed	Nib	Where a square hole is impractical
ASTM A307 carriage	Cup	Square	Imperial equivalent

Use the plate washer or a large flat washer under the nut in timber — a plain washer alone will pull into the wood.

At a glance

Standard	DIN 603
Head	Cup, domed, no drive
Neck	Square, same across flats as the bolt diameter
Thread form	Metric coarse, ISO 68-1
Tolerance	6g
Matching nut	DIN 934 · ISO 4032
Washer in timber	Plate washer or large flat washer
Long neck version	DIN 605
Imperial equivalent	ASTM A307 carriage bolt

Supply

Imported and held in stock, sourced from established mills and supplied from our warehouse in Umm Al Quwain.

Anchor bolts, studs and plate washers are manufactured at our own plant. This item is not.

Materials and finish

Carbon steel	Plain, zinc plated, hot-dip galvanized
Stainless	A2-70, A4-80
High tensile	8.8 to order
Certification	Mill certificate on request

Testing

Dimensional and thread inspection is carried out in our own plant on calibrated instruments. Tensile, hardness and chemical testing is carried out by independent UAE-accredited laboratories.

Reference only

This datasheet is published for reference. Dimensions and property values are reproduced in good faith from published standards, but for design, verification or contractual purposes always refer to the current issue of the original standard.

If a figure here conflicts with the standard, the standard governs.

Need a quotation?

Send the size, length, class, finish and quantity. Tell us whether the hole is square or the bolt goes into timber.