Coach Screws Manufacturer in India | DIN 571 Hex Head Wood Screws

Overview

DIN 571 Hex Head Wood Screws (Coach Screws): Manufacturer & Distributor

A coach screw is a big wood screw with a hexagon head. It is driven with a spanner into a pilot hole and clamps a bracket, plate or board to timber from one side, with no nut.

Exotic Alloy manufactures coach screws in Mumbai, India, for timber builders, deck and fencing contractors, carpenters and pallet makers. We supply across India and to Ireland, the UK, Europe, the Gulf and Africa. Heads are cold forged and threads rolled; steel screws are zinc plated or hot-dip galvanized.

Metric and inch

This page covers metric DIN 571 coach screws and the Eurocode 5 way of rating them. For inch lag screws to ASME B18.2.1 and the US NDS withdrawal method see lag bolts; for screws with a machine thread on one end see hanger bolts.

DIN 571 4 to 20 mm Gimlet point Galvanized A2 / A4

Coach screw at a glance

Head: Hexagon, spanner 7–30 mm
Thread: Wood thread, b ≥ 0.6 l, gimlet point
Length: Under the head
Fixing: One side, into a pilot hole
Design: EN 1995-1-1 with EN 14592 values
Related: Lag bolts, hanger bolts, washers

DIN 571 coach screw 10 × 100, drawn to scale, with a head end view. Thread profile schematic.

Specification

Coach Screw Specification

The range we manufacture and supply.

StandardDIN 571:2016; EN 14592 CE marked versions to order

Size range4, 5, 6, 7, 8, 10, 12, 16 and 20 mm

ThreadWood screw thread, b ≥ 0.6 l, gimlet point

Lengths16–200 mm (DIN 571 table), longer to order

HeadHexagon, s 7–30 mm; flange or washer heads to order

SubstratesSolid timber, glulam, LVL; steel or timber fixtures

MaterialsCarbon steel; stainless A2 (304) and A4 (316)

FinishZinc plated, hot-dip galvanized; stainless plain or passivated

CertificationMill certificate; EN 10204 3.1; DoP for EN 14592 screws

PackingBoxes, buckets, kits with washers

Coach screw or bolt?

Coach Screw vs Through-Bolt vs Carriage Bolt

Three ways to fix to a timber beam.

A coach screw needs access to one side only. Bolts need a nut on the far side but carry more load when both sides are reachable.

Fastener	Access	Holds by	Best for
Coach screw	One side	Wood thread in the timber	Brackets, ledgers, posts to walls
Hex bolt + nut	Both sides	Clamping through the timber	Heavy beams, frames
Carriage bolt + nut	Both sides	Clamping; neck locks in the wood	Smooth, tamper-resistant faces
Lag screw (inch)	One side	Wood thread	US-designed projects, NDS values

Dimensions

Coach Screw Dimensions & Weights (DIN 571)

DIN 571 heads from 4 to 20 mm at the same scale, with the spanner size.

d nominal	d min	s across flats spanner	k head height	e across corners min	Thread length b ≥ 0.6 l	Lengths in DIN 571 mass table
4	3.52	7	2.8	7.5	0.6 × l	16–40 mm
5	4.52	8	3.5	8.63	0.6 × l	16–50 mm
6	5.52	10	4	10.89	0.6 × l	20–80 mm
7	6.42	12	5	13.07	0.6 × l	to order
8	7.42	13	5.5	14.2	0.6 × l	25–100 mm
10	9.42	17	7	18.72	e.g. l 100 → b ≥ 60	30–100 mm
12	11.3	19	8	20.88	0.6 × l	35–120 mm
16	15.3	24	10	26.17	0.6 × l	50–160 mm
20	19.3	30	13	32.95	0.6 × l	60–200 mm

DIN 571:2016, mm. Thread length at least 0.6 times the nominal length, measured under the head.

l, mm	d 4	d 5	d 6	d 8	d 10	d 12	d 16	d 20
20	2.01	3.42	5.02	–	–	–	–	–
30	2.81	4.62	6.62	12.9	23.6	–	–	–
40	3.51	5.82	8.22	15.6	28	39.2	–	–
50	–	7.03	9.64	18.2	32.1	45.4	84.1	–
60	–	–	11.2	20.9	36.5	51.8	94.9	165
80	–	–	14.32	26.5	45.2	64.5	118	201
100	–	–	–	32	54	77.1	141	238
120	–	–	–	–	–	89.5	163	275
160	–	–	–	–	–	–	209	348
200	–	–	–	–	–	–	–	421

DIN 571 approximate mass, kg per 1,000 pieces (steel, 7.85 kg/dm³), selected lengths; stainless is about the same.

d	Core d₁	Shank d_s	Head s / k	Pre-drill d₀ softwood	Hole in steel d_0,steel	f_ax,k N/mm², ρ_a 370	f_head,k N/mm², ρ_a 350	Tension R_tens,k kN	M_y,k N·m
6	4.2	5.4	10 / 4	4	6.5	21.9	22.7	9.19	11.9
8	5.6	7.3	13 / 5.5	5.5	8.5	21	20.9	13.49	25
10	7.2	9.5	17 / 7	7	10.5	18.3	21.8	20.73	44.7
12	9.2	11.5	19 / 8	8.5	12.5	15.8	22.9	25.06	71.9

Declared values of one CE marked EN 14592 hex head wood screw with DIN 571 heads and 0.6 L thread (manufacturer data sheet). Other products declare their own values; design with the values of the screw you buy.

Pre-drilling

How to Pre-Drill & Fit a Coach Screw

A clearance hole in the fixture, a pilot hole in the timber, and the whole thread in the timber.

Coach screws over 6 mm are pre-drilled. The pilot hole lets the thread form without splitting the timber; too small and the screw shears or splits the wood, too large and it strips. Drive with a spanner or impact driver and stop when the head seats on its washer.

The thread must sit in the timber that holds the point, and for design to EN 1995-1-1 the threaded penetration should be at least six screw diameters.

Screw d	Pilot, softwood	Hole in steel	Min. thread in timber
6 mm	4 mm	6.5 mm	36 mm (6d)
8 mm	5.5 mm	8.5 mm	48 mm (6d)
10 mm	7 mm	10.5 mm	60 mm (6d)
12 mm	8.5 mm	12.5 mm	72 mm (6d)

Hole sizes declared for one EN 14592 screw; follow your screw’s declaration.

Load capacity

Withdrawal, Head Pull-Through & Tension (EN 1995-1-1)

Longer screws hold more, until the head pulls through. Through a timber part, head pull-through is often the limit; on a steel plate it does not apply.

An axially loaded coach screw can fail in three ways: the thread pulls out of the timber (withdrawal), the head pulls through a timber part (head pull-through), or the screw breaks (tension). The lowest governs.

EN 1995-1-1 uses values declared by the screw maker: withdrawal = f_ax,k × d × l_ef × k_d × (ρ_k/ρ_a)^0.8, with k_d = d/8 up to 1, and head pull-through = f_head,k × d_h² × (ρ_k/ρ_a)^0.8, for a screw at right angles to the grain.

Size d × L	Thread L_g 0.6 L	Withdrawal R_ax,k kN	Head pull-through R_head,k, kN	Tension R_tens,k, kN	Governs
6 × 60	36	3.39	2.27	9.19	head pull-through
6 × 90	54	5.09	2.27	9.19	head pull-through
6 × 140	84	7.92	2.27	9.19	head pull-through
8 × 60	36	5.79	3.53	13.49	head pull-through
8 × 120	72	11.57	3.53	13.49	head pull-through
8 × 200	120	19.28	3.53	13.49	head pull-through
10 × 80	48	8.40	6.30	20.73	head pull-through
10 × 140	84	14.70	6.30	20.73	head pull-through
10 × 200	120	21.01	6.30	20.73	head pull-through
12 × 120	72	13.06	8.27	25.06	head pull-through
12 × 200	120	21.76	8.27	25.06	head pull-through
12 × 260	156	28.29	8.27	25.06	head pull-through

Our calculation, characteristic values, ρ_k 350 kg/m³, thread 0.6 L fully in the timber; it reproduces the maker’s published table within 0.5 %.

Calculator

Coach Screw Axial Capacity Calculator

Pick the screw and length, the fixture thickness and the timber, then the service class and load duration for a design value.

Screw & joint

Diameter d

Length L, mm

Fixture thickness, mm

Timber ρ_k, kg/m³

Service class

Load duration

Head bears on

Our calculation, EN 1995-1-1 method for one screw at 90° to the grain, using the declared values of one EN 14592 hex head wood screw (d 6–12). Design R_d = min(k_mod × R_k / 1.3; R_tens,k / 1.25). Not a substitute for an engineer’s design with your product’s values.

Result

3.53

kN characteristic

1.95

kN design R_d

Thread in timber l_ef:60 mm

Withdrawal R_ax,k:9.64 kN

Head pull-through:3.53 kN

Tension R_tens,k:13.49 kN

Pilot / steel hole:5.5 / 8.5 mm

Weight (DIN 571):32 g each

Materials

Coach Screw Materials & Finishes

Material	Finish	Best for
Carbon steel	Zinc plated	Indoor, dry timber
Carbon steel	Hot-dip galvanized	Outdoor work, fencing, treated timber
A2 stainless (304)	Plain, passivated	Decks, cladding, visible fixings
A4 stainless (316)	Plain, passivated	Coastal, marine, pools, chemical plant

Acidic timbers such as oak and some preservative treatments corrode plain and zinc-plated steel faster; use hot-dip galvanized or stainless screws there and follow the timber or treatment supplier’s advice.

Carbon steel

Zinc plated

Indoor fixing.

1018 1022

Galvanized

Hot-dip

Outdoor timber.

Coatings

Stainless A2

304

As in the photo.

304

Stainless A4

316

Coastal and marine.

316

Manufacturing

How Our Coach Screws Are Made

1

Wire

Steel or stainless wire, certified by heat.

2

Heading

Hexagon head cold forged and trimmed.

3

Pointing

Gimlet point formed.

4

Thread rolling

Wood thread rolled to 0.6 l or more.

5

Finishing

Zinc plating, hot-dip galvanizing or passivation.

6

Inspection

Head, thread and coating checked, packed by lot.

Applications

Where Our Coach Screws Are Used

Timber framing

Ledgers, joist hangers and brackets.

Decks & docks

Stainless or galvanized, outdoors.

Fencing & gates

Rails, hinges and post fixings.

Play & garden

Play frames, pergolas and furniture.

Pallets & crates

Heavy packing and skids.

Steel to timber

Plates, angles and mounting rails.

Quality & testing

Coach Screw Inspection & Certification

Check	Method	Applied to
Head s, k, e	Callipers to DIN 571	Every lot
Thread length	b ≥ 0.6 l	Every lot
Thread and point	Profile and visual check	Every lot
Coating	Thickness gauge; ISO 10684 for hot-dip galvanizing	Galvanized lots
Driving	Trial drive into timber	Every lot
Material	PMI / chemical analysis	Stainless lots

Every shipment includes

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

On request

EN 10204 3.1 certificate
Declaration of performance (EN 14592 screws)
Coating thickness report

FAQ

Coach Screw Questions, Answered

A heavy wood screw with a hexagon head, also called a hex head wood screw or lag screw, turned in with a spanner. Metric coach screws follow DIN 571 from 4 to 20 mm; the thread is at least 0.6 times the length and ends in a gimlet point.

It is the same type of fastener: coach screw is the British and European name, lag screw the American one. DIN 571 coach screws are metric; ASME B18.2.1 lag screws are inch sizes with different heads and threads, so the two are not interchangeable.

For DIN 571: 7 mm for a 4 mm screw, 8 mm for 5, 10 mm for 6, 12 mm for 7, 13 mm for 8, 17 mm for 10, 19 mm for 12, 24 mm for 16 and 30 mm for 20.

Coach screws over 6 mm need pre-drilling. One EN 14592 maker specifies a 7 mm pilot hole in softwood for a 10 mm screw, about 70 % of the diameter, and a 10.5 mm hole in a steel plate. Follow the declaration of the screw you use.

It depends on the screw's declared values, the timber density and the thread length in the timber. With the EN 1995-1-1 method and the declared values of an EN 14592 screw, an 8 × 100 mm screw in 350 kg/m³ softwood has 9.64 kN characteristic withdrawal but only 3.53 kN head pull-through through a timber part, so the head governs unless it bears on a steel plate.

DIN 571 sets dimensions only. For load-bearing timber structures in Europe, use screws CE marked to EN 14592 or with a European Technical Assessment, which declare the strength values used in design.

Length is measured under the head. Choose it so the whole thread, 0.6 times the length, sits in the timber that holds the point: with a 40 mm fixture, a 100 mm screw puts its 60 mm thread in the timber. EN 1995-1-1 also asks for a threaded penetration of at least 6 times the diameter.

Carbon steel, zinc plated for indoor use or hot-dip galvanized for outdoor and treated timber, and A2 or A4 stainless steel, like the screws in our photo, for decks, coastal and chemical environments.