Why is the Gravlock coupler used in pairs?

The Gravlock is a girder clamp designed to grip an I-beam flange. One coupler grips the flange from one side; the paired coupler grips from the other side. Together they lock around the flange to create a secure connection. A single Gravlock cannot function on its own, the pair is the complete unit. The WLL of 600kg applies to the pair, not to each individual coupler.

What tube diameter does the Gravlock coupler fit?

The Doughty Gravlock Coupler is designed for 48mm diameter tube, which is the standard for entertainment and stage rigging. It attaches that tube to I-beam flanges up to 45mm wide.

Can I mix Gravlock and standard couplers in the same rig?

Yes. Gravlock Couplers are used for tube-to-steelwork connections and standard half couplers are used for tube-to-tube connections. A typical touring rig will use both, Gravlocks to attach bars to the venue's I-beam structure, and half couplers throughout the rest of the rig. The two types are complementary, not interchangeable.

What is the load rating of the Doughty Gravlock Coupler?

The Doughty Gravlock Coupler has a Working Load Limit (WLL) of 600kg per pair. This rating applies to the pair of couplers used together, it is not the rating of a single coupler. Always use Gravlock Couplers in pairs as specified.

Is the Gravlock coupler suitable for outdoor events?

The Gravlock Coupler is made from steel and is designed for professional rigging environments. For outdoor events with exposed steelwork, it can be used where I-beam flanges are accessible and the flange width is within the 45mm specification. As with all steel rigging hardware, check for corrosion and wear before use and ensure safety bonds are fitted on all suspended loads.

Doughty Gravlock Coupler vs Standard Half Coupler: Which Should You Choose?

MTN Team·July 14, 2026

The Gravlock Coupler and the standard half coupler are both Doughty staples but they serve different purposes. This guide explains the differences and when each is the right choice.

Doughty Gravlock Coupler vs Standard Half Coupler: Which Should You Choose?

Both the Gravlock Coupler and the standard half coupler are Doughty products used in entertainment rigging. If you have only encountered them in a catalogue, the difference is not immediately obvious: both clamp a 48mm tube and both are used in stage rigging environments. But they are designed for fundamentally different applications, and using the wrong one can create either a security risk or an unnecessarily expensive rig.

This guide explains what each coupler is, its verified specifications, and which one is right for your specific setup. Both are available at MTN Shop.

What is a Half Coupler?

A half coupler, also called a wrap-around clamp, is a rigging clamp that fully wraps around a tube and is secured with a bolt. It is called a half coupler because it represents one half of a full coupler, two half couplers together form a full tube-to-tube connection.

Half couplers fit the standard 48mm to 51mm entertainment tube diameter and are used across theatre, concert touring, broadcast studio, and corporate event rigging. They are the most common clamp type for attaching lighting bars to truss, securing tube to tube at an angle, and building structural elements in a rig.

Doughty makes half couplers in both fixed and swivel versions. The fixed version holds the tube at a fixed angle relative to the clamp body. The swivel version allows rotation, which is useful when the tube needs to be positioned at a variable angle after installation.

Best for: fixed venue installations, standard rigging applications where tube is attached to tube or truss, situations where a large number of couplers are needed at lower cost per unit.

Doughty Half Coupler: 50mm£22.64 View

What is the Gravlock Coupler?

The Doughty Gravlock Coupler is a steel girder clamp designed for a specific and different purpose: attaching a 48mm tube to an I-beam flange up to 45mm wide. It is not a tube-to-tube clamp, it is a tube-to-steelwork clamp.

The Gravlock is made from steel and must be used in pairs, with one coupler on each side of the I-beam flange. The WLL (Working Load Limit) is 600kg per pair. Each coupler grips the flange from below and the pair lock together to create a secure connection that is fast to install and remove.

The self-locking mechanism is the key feature. Once the pair are positioned on the flange and tightened, the design resists loosening under vibration and load, making it particularly well suited to touring environments where the same connection is made and broken repeatedly across many venues.

Best for: attaching 48mm tube to steel I-beam structures in venues, touring productions that rig to building steelwork, situations where a fast and secure connection to structural steelwork is required.

Doughty Gravlock Coupler per pair£51.50 View

Doughty Gravlock vs Standard Half Coupler: Side-by-Side Comparison

Feature	Standard Half Coupler	Doughty Gravlock Coupler
Primary use	Tube-to-tube or tube-to-truss	Tube-to-I-beam flange (steelwork)
Material	Steel or aluminium	Steel
Used individually or in pairs	Individually	Must be used in pairs
WLL / SWL	750kg	600kg per pair
Tube diameter	48-51mm	48mm
Flange compatibility	Not applicable	I-beam flanges up to 45mm
Installation speed	Standard bolt tightening	Fast: self-locking design
Best for	Fixed venues, standard tube rigs	Touring to steel-framed venues
Cost per unit	Lower	Higher: sold as pairs

When to Choose the Gravlock Coupler
The Gravlock is the right choice when you are rigging to structural steelwork, specifically I-beam flanges. This is a common situation in touring, where productions visit venues with exposed steel roof structures and need to attach 48mm tube directly to the building's beams.

Three situations where the Gravlock is the clear choice:

Exposed I-beams in touring venues
Many theatres, concert halls, and arenas have accessible I-beam structures. The Gravlock was designed for exactly this: fast, secure, repeatable attachment to structural steelwork across different venues.
Speed of rigging matters
The self-locking mechanism is faster to install and remove than a standard bolt-tightened clamp. On a tight build schedule, the difference across an entire rig adds up.
The WLL is a requirement
At 600kg per pair, the Gravlock provides a higher load rating than most standard half couplers. For heavy loads on steelwork, this matters. Always fit a safety bond on any fixture or bar attached via Gravlock couplers, as with any primary rigging fixing.
When to Choose a Standard Half Coupler
The standard half coupler is the right choice for the majority of rigging applications where you are connecting tube to tube or tube to truss, which covers most venue installations, theatre rigging, and studio setups.

Fixed venue installations
Where the rig is installed once and stays in place, the half coupler's simplicity and lower cost per unit makes it the practical choice for large quantities.
Tube-to-tube connections
The Gravlock is designed for steelwork, not tube-to-tube. For standard bar-to-truss or tube-to-tube connections, a half coupler is the correct tool.
Interchangeability with existing stock
If your venue or touring company already uses half couplers throughout the rig, adding more of the same type maintains consistency and avoids mixing systems.

View Featured Products

Doughty Gravlock Coupler per pair£51.50

Doughty Gravlock Swivel Coupler per pair£51.50

Doughty Half Coupler: 50mm£22.64

Doughty Half Coupler 50mm- Super Lightweight£10.00

Doughty Half Coupler: 60mm Mammoth Clamp£23.67

Doughty Safety Bonds — 5kg -100kg£3.25

Can You Use Both in the Same Rig?

Yes. A typical touring rig might use Gravlock Couplers to attach the main horizontal bars to the venue's I-beam structure, and standard half couplers throughout the rest of the rig for tube-to-tube connections. The two couplers serve different connection types and are fully complementary.
What you should not do is use a standard half coupler where a Gravlock is specified, a half coupler is not designed to grip an I-beam flange and will not provide a secure connection to structural steelwork. If you are rigging to building steelwork, the Gravlock Coupler is the correct tool for that specific connection.

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Doughty Gravlock Coupler vs Standard Half Coupler: Which Should You Choose?

What is a Half Coupler?

What is the Gravlock Coupler?

Doughty Gravlock vs Standard Half Coupler: Side-by-Side Comparison

View Featured Products

Can You Use Both in the Same Rig?

Frequently Asked Questions

Additional Articles

Doughty Engineering: Why Professionals Choose This Brand for Stage and Studio Rigging

Doughty Clamps Explained: Which One Do You Need for Your Rig?

Doughty Spigots Explained: Female Threads, Adapters and the 16mm Standard

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