What do S235, 80 × 80 mm and 3 mm mean on a spec sheet?

Every spec sheet speaks a language of its own. Ours says S235 steel, 80 × 80 mm tube and a 3 mm headboard panel. To a fabricator those are plain descriptions. To anyone else they're a string of letters and numbers that explain little on their own.

One point first. These terms describe the materials. They aren't load ratings, and none of them tells you how much any piece of furniture can hold. We don't publish load or weight figures for any piece, and nothing on a spec sheet should be read as one. No piece we make is designed to hold a person's weight off the ground, and none must ever be used that way.

S235: the steel grade

S235 is a grade of structural steel defined in a European standard. The letter and the number each mean something specific.

• The S stands for structural. It identifies a steel intended for structural use, such as frames, beams and supports.
• The 235 refers to the minimum yield strength the standard sets for that grade, in megapascals. Yield strength is the stress beyond which a material no longer returns to its original shape.

That number is a property of the material, as defined by the standard. It says nothing about a finished piece of furniture, which depends on its design, its joints and how it's used. A spec sheet that quoted the grade as if it were a rating for the furniture would be misleading, so we don't.

Why choose it? S235 is a widely used structural grade with documented properties. When we say every piece is S235 steel, we're telling you what it's made of, in terms any fabricator would recognise.

80 × 80 mm: the tube

Our frames are built from square steel tube, 80 × 80 mm. That figure is the outside size of the tube's cross-section: each face is 80 mm wide. If you cut through one of our posts, you'd see a square, 80 mm on each side, with a hollow centre.

Square tube gives a frame clean, straight lines and flat faces, which suits the architectural look of our pieces and makes the finish easy to wipe down. The size of the tube is one part of the frame's design; it isn't a measure of what the frame can hold. For any other detail about the tube, such as its wall thickness, ask us.

3 mm: the headboard panel

Most of our beds carry a headboard made from a 3 mm steel panel. The figure is the thickness of the sheet. Each panel is laser-cut with the pattern for its bed: the arcs on Pavilion, the diamonds on Arcadia, the fine grid on Regent, and so on. Axis is the exception, with no headboard pattern at all.

Laser cutting uses a focused beam to cut the steel along a drawn path, which allows fine, precise patterns. The headboard is a decorative panel; it's the part of the bed that sets its character.

Welded D-rings

The restraint points on our frames are D-rings: closed loops of steel shaped like a D. They're welded to the frame, so they're part of the frame itself. Our guide to the difference between a hook and a welded D-ring explains why we use them. For where the rings sit on a particular piece, ask us.

The finish

Every piece is coated. Obsidian, Oxblood, Gilt, Chalk and any RAL colour are powder coat, applied as a dry powder and cured into a hard, even coat, so there are no brush marks and the colour is consistent across the piece. Paint goes on wet. Forge Clear is a clear coat over the steel.

We offer five colours in our library, Obsidian (black), Oxblood (red), Gilt (gold), Chalk (white) and Forge Clear, which keeps the look of the steel itself, or any RAL colour. A coated surface wipes clean with warm water and mild soap; our care guide sets out what to avoid.

How the parts come together

Every piece arrives flat-packed and is assembled at home with fixings, following the printed assembly instructions. The welded D-rings are part of the frame; the rest of the piece is joined by those fixings. That's why every fixing is re-tightened before first use and whenever a piece is moved, and why the frame and its fixings are checked before each use. Our guide to checking your furniture before each scene sets out the routine.

A short glossary

• Structural steel: steel made for frames and supports, defined by a named grade.
• Square hollow section, or square tube: steel tube with a square cross-section and a hollow centre.
• Laser cutting: cutting sheet steel with a focused beam, which allows fine, precise patterns.
• D-ring: a closed loop of steel shaped like a D, used as a restraint point.
• Powder coat: a finish applied as a dry powder and cured into a hard, even coat.
• Clear coat: a transparent coat that shows the material beneath it, as on Forge Clear.
• RAL: a standard colour system in which each colour has its own reference number.
• Flat-pack: delivered as parts, for assembly at home with printed instructions.
• Fixings: the parts that join a flat-packed piece together.

Reading anyone's spec sheet

Whoever you buy from, a few questions help you read a spec sheet well.

• What is the material, and what grade? A named grade is more useful than a general description.
• What are the frame's sections? Square or round tube, solid bar, timber: each has different qualities.
• How are the restraint points attached?
• What is the finish, and how should it be cleaned?
• What does the maker say the piece is not designed for?

Clear answers, with nothing overclaimed, are what to look for. Our guide to questions to ask a restraint furniture maker goes further.

Every piece in our BDSM beds, St Andrew's crosses and BDSM cages collections is S235 steel, coated in the finish you choose, and made to order with a current lead time of 8–14 weeks.