Key Clamp Fittings and Galvanised Tube

Key Clamp Fittings and Galvanised Tube: Sizes, Codes and Stock

Key clamps are malleable iron fittings that lock onto galvanised steel tube with a set screw and a hexagon key. No welding, drilling or threading. We hold Fisher Alvin key clamp fittings and tube in five sizes, 26.9mm to 60.3mm, for handrail, guardrail, barriers, racking, shop fitting and frames of almost any shape. For a complete railing, see our key clamp handrails, supplied as bolt-down kits.

Stock orders go out for next-day delivery, we cut tube to length free, and we quote within one hour, Monday to Friday, 8am to 5pm. Send us a list of codes, a sketch or a photo and our free design service will list the parts for you.

Key Clamp Sizes

Start with the tube size: the tube is the main structural component of any key clamp structure. Fisher Alvin key clamps are made in five sizes, numbered 5 to 9. Each size number matches one tube outside diameter, and every fitting in a size fits every tube of that size. The size is the number after the dash on every fitting code: A2-7 is an A2 short tee for size 7 tube.

Not every fitting is made in every size. The G gradient fittings and the C slope fittings come in sizes 7 and 8 only, and fittings such as the A9 internal connector run from size 6 to 8. Check the sizes on each fitting before you order tube. Our guide on how to choose the right key clamp size goes through the decision in more detail.

How Key Clamps Work

Every key clamp is a casting with one or more sockets. Slide the tube in, tighten the set screw with a hexagon key, and the joint locks. When tightened to 29 ft lb (4.1 kgm), a slip load of 900kg can be obtained on each screw. Fittings with two socket set screws, such as the A12 base plate, give a rigid structural fixing.

• Through or into. Some fittings let the tube pass straight through (the A20 mid corner tee and A22 cross tee keep a post continuous). Others take the tube end only, so you cannot join tube inside them.
• Change it later. Loosen the screw and the joint comes apart, so a frame can be adjusted, extended or taken down. The CA03 add on short tee, CA40 add on 90 degree crossover, A32 clamp on tee and A66 clamp on crossover let you add to a structure without dismantling it.
• Supplied ready to fit. Clamps come with their set screws fitted. Spare A78 screws and the A76 hex key are listed separately: tell us the clamp type and size when you order replacement screws, as there are two thread sizes.

The Fittings You Will Use Most

Each code is the fitting type followed by the size, so A6-8 is an A6 90 degree elbow for size 8 (48.3mm) tube.

A typical guardrail uses the A4 long tee for the top rail and the A22 cross tee for the lower rails on each intermediate post, the A2 and A6 at the ends, the A18 and A20 at corners, and the A12 base plate at the foot of each post.

The Full Range, by Job

Our key clamp range runs well beyond the core tees and elbows. Here is where each family fits.

How to Choose the Right Fittings

1. Start with the use. Size 5 or 6 suits lighter indoor work such as displays, furniture and shop fitting. Size 7 or 8 is the usual choice for handrail, guardrail, barriers and outdoor structures. Size 9 suits heavier posts and frames.
2. Check the fitting exists in that size. If your design needs a slope fitting, you are in size 7 or 8. If it needs an A9 internal connector, you are in size 6 to 8.
3. Check the load. For guardrail, the spacing of the uprights matters as much as the tube size. Use the table below.
4. Choose the finish. Galvanised as standard. Powder coating on request: tell us at quote stage and we build it into the price.
5. Kit or loose. For a standard bolt-down handrail run, our key clamp handrail kits group the parts for you. For anything else, order loose fittings, or send us a sketch and we list them.

Guardrail Upright Spacing

Guardrail load capacity depends mainly on the diameter, wall thickness and spacing of the uprights. The maximum upright centres below are based on the maximum permissible bending moment of the upright tube, for 1100mm high guardrail only, with tube to BS EN 10255.

Maximum upright centres in mm, 1100mm high guardrail. Rails need only be 3.2mm wall and the same diameter as the upright. The design load for your site is usually specified; if it is not, BS 6399 and BS 6180 are the reference documents. This table is a selection aid, not a design. The finished structure must be checked by whoever signs it off.

Read across before you order. On 48.3 x 3.2mm tube, a 1500 N/m design load allows 359mm between uprights against 1496mm at 360 N/m, so the same run needs far more posts.

Fitting Rules Worth Knowing Before You Order

These come from the product data for each fitting. They are the points that most often change an order.

• Joints near a support. Joints made with the A8 or A9 connector should be within 150mm of the nearest support. Neither should join tubes under extreme loads, and the A9 is not for joints under direct tensile load. Do not use an A8 to join a vertical post that supports a guardrail.
• Wall flange is not a post base. The A10 is for handrails that end on a wall. It is not a structural fixing for a guardrail post: use the A12 base plate.
• Base plate orientation. Fix the A12 and G12 with the bolts in line with the applied load, at 90 degrees to the rails.
• Angled bases take light loads. The C59 and C59A set an upright at an angle and should only take light loads. For greater loads, use an A12 with the upright bent to the angle.
• Add-on fittings. Tubes must not be joined within the CA03 or CA40.
• Wall thickness. The A9 internal connector needs tube with a maximum wall thickness of 3.2mm, and the C65G metal end cap only suits 3.2mm wall tube. The A68 plastic cap is the alternative.
• Mesh and infill. Space A70 and A72 mesh clips 450mm apart. Without the horseshoe end they hold other infill up to 10mm thick.
• Side supports. The A16 should not be used for heavy duty applications. On the A14, access to the top fixing hole is restricted, so a threaded stud projecting no more than 25mm from the structure must be fixed first.
• Do not pre-drill. The fittings are galvanised castings and dimensions are guidance only, subject to manufacturing tolerances. Set the fitting in position on site, mark through it, then drill.

Materials, Finish and Standards

• Material. Malleable iron castings, manufactured in excess of BS 6681 (ISO 5922) and BS 2789 (ISO 1083). The A66 clamp on crossover is mild steel.
• Finish. Hot-dip galvanised to BS EN ISO 1461 as standard. Powder coating is available on request.
• Screws. Dacromat coated, case hardened set screws.
• Tube. The fittings are designed for steel tube to BS EN 10255 with a minimum wall thickness of 3.2mm. Fisher Alvin tube in 3.2m and 6.4m lengths conforms to BS EN ISO 1461. See galvanised key clamp tube for lengths and cutting.
• Guardrail and barriers. Building Regulations Approved Document K covers protection from falling, and BS 6180 covers barriers in and about buildings, including loading.
• Accessible handrail. Our DDA fittings are for 42.4mm (size 7) tube, for continuous handrail to the Equality Act 2010 and Building Regulations Approved Document M when configured correctly.

Compliance depends on how the structure is designed, built and used. The duty to check the finished installation sits with whoever signs it off.

Where Key Clamps Are Used

• Handrail and guardrail. Uprights, top rail and mid rail from stock fittings, or a handrail kit for standard runs. Compare modular guardrail with welded.
• Accessible handrail. DDA fittings work with standard key clamps to make a smooth to touch, continuous handrail on 42.4mm tube. See the DDA handrail range and DDA compliant ramps.
• Roof, mezzanine and barriers. Key clamps are used in roof edge protection and in gate openings with self-closing safety gates. The A11 kick plate base plate is popular for fixed handrail on roofs and mezzanines, where tools and materials must not drop from above.
• Racking and storage. A kayak club built its racking from 500 clamps and 300 metres of tube, cut free: read the racking project. A horse owner's rug rack also works as a drying rack: stable storage.
• Shop fitting and furniture. Garment rails, shelving and display stands, mostly in size 6. See shop fit clamps, and square fittings for box section builds.
• Sport, garden and one-offs. Cricket nets, a fruit cage, a parkour frame and a netting frame for a butterfly house. More on the projects page.

How to Order Key Clamps

1. Pick the tube size from the size table.
2. List the fittings by code and size, for example 12 x A22-8. Not sure? Send us a sketch, drawing or photo with measurements and our free design service will draw up the layout and list the parts.
3. Give us the tube lengths you need. We cut them free before despatch.
4. Request a quote, email [email protected] or call 01905 779944. We quote within one hour, Monday to Friday, 8am to 5pm.
5. Delivery is charged at cost and confirmed with your quote, before anything is despatched. Stock orders go out for next-day delivery; orders with tube cut to length can take two to three days.

Why Buy Key Clamps from Fisher Alvin

• In stock. Fittings and tube in all five sizes, with next-day delivery on stock orders.
• Tube cut to length, free. No cutting on site.
• Quote within one hour, Monday to Friday, 8am to 5pm.
• Free design service. Send a sketch and we list every fitting and tube length.
• Experience. Founded in Birmingham in 1912, now based in Cradley Heath, and making key clamp fittings for over fifty years.
• Outside the UK? We have key clamp stockists in many countries and deliver direct where there is no stockist.

Key Clamp Questions

What sizes do key clamps come in?

Five sizes, numbered 5 to 9: 26.9mm, 33.7mm, 42.4mm, 48.3mm and 60.3mm tube outside diameter. Not every fitting is made in every size, so check the fitting before you order tube.

How strong is a key clamp fitting?

When tightened to 29 ft lb (4.1 kgm), a slip load of 900kg can be obtained on each screw. The strength of a finished structure depends on tube size, wall thickness and upright spacing, so check the design against the loads it must carry.

Do I need to weld or drill anything?

No welding, threading or special tools. You tighten the set screws with a hexagon key. Base plates are fixed down with through bolts such as our ANC anchor bolt: set the fitting in position, mark through it and then drill, rather than pre-drilling.

How do I read a key clamp code?

The letters and first number are the fitting type and the number after the dash is the size. A12-8 is an A12 base plate for size 8 (48.3mm) tube.

Which fittings do I need for a guardrail?

Typically an A4 long tee for the top rail and an A22 cross tee for the lower rails at each intermediate post, A2 and A6 fittings at the ends, A18 and A20 at corners, and an A12 base plate at the foot of each post. Upright spacing depends on the design load.

What fittings do I need for stairs or a ramp?

The G gradient fittings and the C slope fittings, made for sizes 7 and 8. Different fittings cover 11 to 30 degrees and 30 to 45 degrees, so tell us the angle or send a drawing.

Can you powder coat key clamps?

Yes. Fittings and tube are hot-dip galvanised to BS EN ISO 1461 as standard, and we can quote for a powder coated finish. Ask at quote stage so it is built into the price.

Can you cut the tube for me?

Yes, free of charge, before despatch. Give us the lengths when you order. Orders with cut tube can take two to three days.

Key Clamp Guides and Related Ranges

Not sure what to order: how to choose the right key clamp size, key clamp fittings versus welding and traditional pipe joining, where key clamp fittings get used, why key clamp handrail fittings suit outdoor work, why key clamp handrails cost less over their life, key clamp handrail systems, why DDA handrails are 42.4mm and the key clamp FAQs.

Related ranges: galvanised key clamp tube, key clamp handrail kits, DDA handrail range, shop fit clamps, square fittings and self-closing gates. Download the brochures, or send us a plan and we will list the parts.