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EN8D Rebar Coupler for TMT Bar Connections

EN8D Rebar Coupler for TMT Bar Connections Specification

Constitute
Standard

Color
Black

Sleeve size
16mm, 20mm, 25mm, 32mm, 40mm - To match TMT Bar

Weight
0.18 Kg, 0.28 Kg, 0.45 Kg, 0.72 Kg, 1.10 Kg Kilograms (kg)

Features
700-750 MPa UTS, Bar-Break Guarantee, 125% fy as per IS 16172:2023, Slip <0.10mm, Type 2 + Class L/H, Saves 15% Steel, No Welding

Technique
Forged, Welded Layher

Product Type
Cuplock System

Material
Steel

Components
Couplers

Diameter
6mm, 20mm, 25mm, 28mm, 32mm, 36mm, 40mm Millimeter (mm)

Width
28mm to 62mm Millimeter (mm)

Length
55mm, 65mm, 75mm, 90mm, 110mm Millimeter (mm)

Thickness
8mm to 15mm Millimeter (mm)

Surface Treatment
Hot Dip Galvanized

Application
Construction

Size
16mm to 40mm

EN8D Rebar Coupler for TMT Bar Connections Trade Information

Minimum Order Quantity
10 Kilograms

Delivery Time
24 Hours

About EN8D Rebar Coupler for TMT Bar Connections

EN8Dl Rebar Coupler for TMT Bar Connections

What is EN8D Material?

EN8D is a medium carbon steel grade under British Standard BS970 - 080M40. It's also written as EN8Dl in market.

It's preferred for couplers because Mild Steel fails under high tensile load, while EN8D gives 650-750 MPa strength with good machinability.

Chemical Composition of EN8D:

Element	%
Carbon (C)	0.40 to 0.45%
Silicon (Si)	0.05 to 0.35%
Manganese (Mn)	0.70 to 0.90%
Sulphur (S)	<=0.06%
Phosphorus (P)	<=0.06%

Types of EN8D Rebar Couplers

All types use same EN8D material, only thread design differs:

a) Parallel Threaded Coupler: Most common. Cold-forged, parallel threads. For standard columns/beams. Complies with IS 16172:2023, ACI 318 Type 1 & 2, BS 8110

b) Taper Threaded Coupler: Tapered threads for easy alignment, better for precast.

c) MBT / Bolted Coupler (Mechanical Bolted): No threading needed. Two TMT bars inserted and bolts tightened till shear-off. Material Grade EN8D Carbon Steel. Ideal for repair work.

d) Cold Forged / Type II Bar-Break Coupler: Bar ends are cold-forged to increase diameter before threading. No reduction in cross-section. Guarantees bar-break failure, not coupler failure.

e) Position Coupler: For places where both bars cannot be rotated.

Technical Specification - Standard Sizes

Manufactured as per IS 16172:2023

Rebar Dia	Coupler Outer Dia (OD)	Coupler Length	Thread Pitch	TMT Grade Compatible
12mm	21mm	45-50 mm	2.5 mm	Fe500 / 500D / 550
16mm	28mm	55-60 mm	3.0 mm	Fe500 / 500D / 550 / 600
20mm	32mm	65-70 mm	3.0 mm	Fe500 / 500D / 550 / 600
25mm	40mm	75-80 mm	3.0 mm	Fe500 / 500D / 550 / 600
32mm	50mm	90-95 mm	4.0 mm	Fe500 / 500D / 550
40mm	62mm	110-120 mm	4.0 mm	Fe500 / 500D

Standard Sizes are 12mm,16mm,20mm,25mm,32mm,40mm with OD ranging 21mm to 62mm.

Surface: Black / Self-colour / Hot Dipped Galvanized
Thread Type: Parallel thread (rolled or cut)
Tolerance: +/- 1%

How It Works - Why Better Than Lapping?

Lap splicing needs 40-60x dia overlap. For 25mm bar, that's 1 to 1.5m extra steel per joint. Coupler eliminates that.

Under IS 16172, a full-strength coupler must develop at least 125% of specified yield strength (fy) of parent bar. Failure must happen in the TMT bar, not in coupler.

Benefits:

Saves 10-15% steel
Prevents congestion, honeycombing - concrete flows easily
Seismic safe - tested for cyclic loading (Zone III, IV, V)
Faster work, no welding
Works where lapping impossible - piles, precast, tight formwork

Manufacturing Process at Surya Engineering

Raw material check - EN8D billets test for C=0.40-0.45%
Cold forging / hot forging to required OD
CNC machining of internal parallel threads
GO / NO-GO gauge inspection for every batch
Anti-rust coating / Galvanizing

We manufacture couplers with tensile strength up to 700-750 MPa with no reduction in cross-sectional area.

Quality Testing as per IS 16172:2023

Every batch should have:

Static Tensile Test: UTS >= 625 MPa min, must achieve bar break
Slip Test: Total slip < 0.10 mm
Low-Cycle Fatigue: 10,000 cycles alternate tension/compression
High-Cycle Fatigue (for Class H): S-N curve test for bridges/towers
Chemical Composition Test

Applications

High-rise buildings in Mumbai/Thane, Metro projects, bridges & flyovers, dams, industrial floors, foundation piling, precast elements, seismic retrofitting.

FAQ

1. Why EN8D specifically, why not Mild Steel or EN8?
MS has UTS 410-450 MPa, it will strip before a Fe550 TMT bar yields. EN8D is 080M40 medium carbon steel with C 0.40-0.45%. That gives 650-750 MPa UTS after forging, without heat treatment. EN8 has higher sulphur, EN8D is cleaner grade - better for threading and GO/NO-GO consistency.

2. Is EN8D weldable? Can I weld a coupler to a plate?
No. At 0.40%+ carbon, Carbon Equivalent (CE) is >0.60. Welding will cause HAZ cracking. If you need weldable coupler, you need to use EN8D coupler + weldable anchor head, never weld directly on coupler body.

3. Why does the coupler have higher strength [700 MPa] than the TMT bar [550/600 MPa]?
As per IS 16172:2023, splice must develop 125% of fy of bar. Failure must be Bar-Break, not Coupler-Break. If coupler is same strength as bar, failure will be at threads. EN8D is intentionally over-strength.

4. Cut threads vs Rolled threads - which is better for fatigue?
Cut threads cut the grain flow, rolled threads form the grain flow. Rolled threads give 30-40% better fatigue life. That's why IS 16172 Class H [high-cycle for bridges] always requires rolled threads. Cut threads are only allowed for Class L.

5. Cold-forged vs Hot-forged coupler - difference in grain structure?
Cold forging enlarges bar end diameter by 15-20% before threading. So threaded cross-section is BIGGER than parent bar. No area loss. Hot-forged couplers are made from solid EN8D bar drilled and threaded - grain is discontinuous. Cold-forged gives true bar-break.

6.Can I use a standard coupler in compression? Does length change?
Coupler in compression works even better than tension. But you still need same engagement. Common mistake: contractors think compression needs less engagement and leave gap in centre. Centre gap >3mm creates eccentric load and buckling of bar ends inside coupler.