1
100 mm sphere test
The rule that no opening in guarding should let a 100 mm sphere pass where children under five may be present. The same guidance says to avoid horizontal rails that children can climb.
Also called: child-safe gap rule
2
2B finish
The standard smooth, slightly dull cold-rolled stainless sheet surface. It is the default mill finish, often hidden behind further polishing or coating when appearance matters.
Also called: mill finish, cold-rolled bright (matt)
3
304 stainless steel
The standard general-purpose stainless grade for interiors and mild exteriors. It has no molybdenum, so it is less resistant to salt and chloride than 316.
Also called: 1.4301, A2 (fasteners), 18/8, 304L (low carbon)
316 stainless steel
A stainless grade with added molybdenum for better resistance to salt, chlorides and pitting. It is the usual upgrade for coastal, pool-side and wet-area use, but is not immune to staining or to cracking in indoor pool halls.
Also called: 1.4401, A4 (fasteners), marine grade
A
Anodising
An electrochemical process that thickens the natural oxide layer on aluminium, making it harder and more corrosion resistant while keeping the metal visible. Colour comes from dye or from the process itself, and batches can vary.
Also called: anodised aluminium, anodic oxidation
Anodising quality (AQ)
Aluminium sold with controlled surface and composition so it anodises evenly. Ordinary alloy of the same number can show streaks and colour variation after anodising.
Also called: AQ sheet, architectural anodising grade
Antique finish
A darkened, toned-down finish meant to look aged. Makers use 'antique', 'aged' and 'burnished' inconsistently, so a sample is needed.
Also called: antiqued, aged, burnished, oil-rubbed bronze
Austenitic stainless steel
The most common family of stainless steel, containing chromium and nickel. It forms and welds well, and in its normal annealed state it is non-magnetic. Grades 304 and 316 belong to this family.
Also called: 300-series stainless, 18/8 (loosely)
B
BA (bright annealed) finish
A smooth reflective stainless surface produced by annealing in a protective atmosphere. It is bright but not a true polished mirror.
Also called: 2R, mirror-like mill finish
Bead blasting
Impacting the surface with fine glass beads to give an even, non-directional matt texture with low reflectivity. It is not covered by the EN 10088-2 finish codes, so describe it and agree a sample.
Also called: bead-blasted finish, shot blasting (different medium)
Blackening
Chemically or thermally darkening steel to a black or dark grey, usually then sealed with wax or lacquer. It is a surface conversion, not a thick coating.
Also called: black oxide, gun-blued steel, blackened steel
Brass
A copper and zinc alloy. More zinc gives a paler, harder metal; sheet, bar and casting grades differ in workability, colour and lead content, so name the alloy, not just 'brass'.
Also called: yellow brass, CW508L / CZ108, CW614N / CZ121
Bronze
A copper alloy usually with tin or another main addition instead of zinc, giving a darker, browner metal. In interiors the word is often used loosely for a bronze-coloured finish on brass or steel.
Also called: architectural bronze, phosphor bronze, silicon bronze
BS 4800
A British Standard colour reference for building paints. Its current status and cross-references to RAL should be checked before citing.
Also called: BS colour chart
C
Chloride stress corrosion cracking
Sudden cracking of stressed stainless parts exposed to chlorides, notably hangers and bolts in warm chlorinated indoor pool halls. Treat critical suspended fixings as an engineering decision.
Also called: SCC, pool hall cracking
Cold-rolled steel
Steel further rolled at room temperature after the oxide is removed, giving a smoother, flatter, more precise sheet that takes paint and powder well. It looks flatter than hot-rolled steel when blackened.
Also called: CR, cold-reduced steel, DC01
Corrosivity category (C1-C5)
A classification of how aggressive an environment is for coated steel, from dry heated interiors up to marine and industrial sites. Coating systems and expected life are matched to it.
Also called: ISO 12944 category, CX
Crevice corrosion
Corrosion that starts in tight gaps where moisture and salts get trapped, such as under washers or in woven mesh. Seal or avoid the gap.
Also called: crevice attack
Critical location (glazing)
Areas of glass in doors, side panels and low windows where people are likely to be hit by or fall into it, so safety glass or protection is required. Approved Document K maps them with heights of 1500 mm and 800 mm.
Also called: safety glazing zone
D
Declaration of Performance (DoP)
A document in which a manufacturer declares the performance of a construction product. It sits alongside the mark, not in place of it.
Also called: DoP
Delta E (colour difference)
A number describing how far apart two colours are as measured by a spectrophotometer. Use only with a tolerance that comes from a standard or an agreed sample.
Also called: dE
Dezincification
A corrosion process in which zinc leaches out of some brasses in wet or aggressive conditions, leaving a weak, porous copper-rich structure. Dezincification-resistant grades exist for wet areas.
Also called: DZR brass (dezincification-resistant)
Duplex coating system
A hot-dip galvanised surface that is then painted or powder coated for extra life and colour. Not related to duplex stainless steel.
Also called: galvanise-and-paint
Duplex stainless steel
A stainless family with a mixed structure, giving higher strength than austenitic grades and good resistance to chloride attack. It is magnetic and sits between ferritic and austenitic grades for forming. Do not confuse it with a 'duplex system' of galvanising plus paint.
Also called: 2205, 1.4462, lean duplex
E
Electroplating
Depositing a thin metal layer, such as nickel, chrome or gold, onto another metal using electric current. Cheap and bright, but the layer is thin and can wear through at contact points.
Also called: plating, chrome plating, gold plating, nickel plating
Electropolishing
An electrochemical process that removes a thin surface layer from stainless steel, leaving it smoother, brighter and cleaner. It is not the same as mechanical buffing.
Also called: electropolish
EN 10088-2 finish code
The European letter-number codes for stainless sheet surface finishes. Mechanical polishing and brushing fall under the G, J, K and P codes.
Also called: 1D, 2B, 2R, 2J, 2G, 2K, 2P (verify), mill and polish codes
Euroclass A1 / A2-s1,d0
European reaction-to-fire classes for materials. A1 is non-combustible; A2-s1,d0 is nearly so with very low smoke and no flaming droplets. Balcony rules on tall residential buildings point to these classes.
Also called: non-combustible, limited combustibility
Execution class (EXC1-EXC4)
A level of fabrication control and inspection under BS EN 1090 for structural steelwork, chosen from the consequences of failure and the type of building. EXC2 suits most UK buildings.
Also called: EXC2
Expanded metal
Sheet slit and stretched into a diamond-shaped mesh with no waste. It is one piece, unlike woven wire mesh.
Also called: expanded mesh
F
Ferritic stainless steel
A stainless family with chromium but little or no nickel. It is magnetic and less formable than the austenitic grades, and some grades are used where cost matters or nickel is unwanted.
Also called: 400-series stainless, 430, 444
G
Galvanic corrosion
Accelerated corrosion of one metal where it touches a different metal in the presence of moisture. A small part of the more reactive metal against a large area of the nobler metal is the worst case.
Also called: bimetallic corrosion, dissimilar-metal corrosion
Gauge (SWG / BWG)
An old numbering system for sheet and wire thickness where a higher number is thinner. Different systems and metals give different thicknesses for the same number, so always state mm.
Also called: gauge number, ga.
General tolerance class
A default tolerance applied to dimensions on a drawing that carry no individual tolerance. Drawings without one are considered incomplete.
Also called: ISO 13920, ISO 2768
Gloss unit (GU)
A measured value of how shiny a surface is, usually at 60 degrees. Trade words like matt, satin and gloss are not fixed bands, so give a GU target and tolerance.
Also called: gloss level, sheen
Going and rise
The going is the horizontal depth of a step, the rise its vertical height. Approved Document K gives limits by stair category and says twice the rise plus the going should be about 550 to 700 mm.
Also called: tread depth, riser height
Grain direction
The direction of the lines left by brushing or polishing. Vertical grain is easier for rain and cleaners to wash than horizontal grain, and mismatched directions across panels are very visible.
Also called: finish orientation, brushing direction
Ground-flush weld
A weld ground and blended until the joint reads as continuous metal, then refinished to match. It costs labour and needs the surface finish specified.
Also called: dressed weld, invisible weld
Guarding
Barrier at an edge to prevent falls, such as on stairs, landings and balconies. In Approved Document K the minimum height depends on building type and location.
Also called: balustrade, barrier (in vehicle areas), guard
H
Handrail
A rail to hold on to along stairs or ramps. Approved Document K sets its height range from the pitch line or floor, and requires both sides on wider stairs.
Also called: grab rail
Heat tint
The straw-to-blue discolouration around a weld on stainless steel. It lowers corrosion resistance and is removed by pickling or mechanical cleaning.
Also called: weld discolouration, oxide colour
Hot-dip galvanising
Dipping fabricated steel in molten zinc to give a thick protective coating. The standard sets minimum thicknesses by steel thickness, for example 85 um mean on steel over 6 mm.
Also called: galvanised steel, HDG
Hot-rolled steel
Steel rolled while hot, leaving a darker, rougher oxide skin (mill scale) and slightly less precise sizes. It is the usual base for 'blackened steel' looks.
Also called: HR, mill-finish steel
J
Juliet balcony
A guard across a door opening with no usable balcony platform. For building regulations it is guarded like an external balcony.
Also called: Juliette balcony, French balcony
L
L grade (low carbon stainless)
A stainless grade with lower carbon content, preferred for welded sections thicker than about 6 mm so the weld zone keeps its corrosion resistance.
Also called: 304L, 316L, 1.4307, 1.4404
Lacquer (on metal)
A clear protective coat over polished or patinated metal to slow tarnishing. It can wear or yellow in high-touch areas and eventually needs stripping and reapplying.
Also called: clear coat, lacquered brass
Laser cutting
Cutting sheet with a focused laser beam, good for fine detail and clean edges on thin to medium thickness. Heat can discolour some metals at the edge.
Also called: fibre laser, profile cutting
Liquid metal finish
A sprayed or cast metal-filled coating that gives a metallic look on a non-metal or metal base. It is not the same as solid sheet or a plated finish.
Also called: cold-cast metal, metal-effect coating
Living finish
A metal surface left unsealed so it keeps changing with touch, moisture and time. Clients should be told this in writing.
Also called: unlacquered finish, natural finish
M
Mild steel
Ordinary low-carbon steel: strong, cheap and easy to weld, but it rusts unless oiled, waxed, coated or deliberately blackened. In specifications it should be named by grade, such as S275.
Also called: carbon steel, low-carbon steel, black steel
Mill certificate (3.1)
A document from the metal producer stating the grade and test results of the batch. Asking for a '3.1' certificate is how a specifier proves the material is what the drawing says.
Also called: mill test certificate, EN 10204 3.1, material certificate
Mill scale
The grey-blue iron oxide layer left on steel after hot rolling. Keeping it gives blackened steel its dark, variable look; removing it by pickling gives a plain grey surface.
Also called: black scale, hot-rolled skin
Mirror polish
A highly reflective stainless or metal surface made by progressive polishing. It shows fingerprints, scratches and weld marks readily.
Also called: No.8 finish, mirror finish, super mirror
N
Nickel silver
A copper alloy containing nickel and zinc but no silver. It gives a pale, silvery-gold metal that polishes well and tarnishes less than brass.
Also called: German silver, alpaca, maillechort
No.4 finish
A fine, directional brushed stainless surface. It is a common architectural finish but the word 'brushed' alone does not define it; give a grit or roughness and a grain direction.
Also called: brushed stainless, satin stainless, directional grain finish, hairline (similar)
NSSS (National Structural Steelwork Specification)
The UK model specification for steelwork contracts, incorporating BS EN 1090 obligations. The 7th edition main body is written for EXC2.
Also called: NSSS 7th edition
O
Oil canning
Visible waviness or rippling in flat metal sheet, caused by stresses, thin material, restraint or temperature movement. Thicker sheet, backing and fixing design reduce it.
Also called: panel waviness
P
Passivation
Treating stainless steel with acid, such as nitric or phosphoric, after fabrication to improve its resistance to pitting. IMOA says it is worthwhile where the steel's sulphur content is above 0.005%.
Also called: passivating
Patina
A surface layer that forms on copper alloys with exposure and changes their colour, from brown towards grey-green over years. Different alloys develop it at different rates.
Also called: verdigris (green), tarnish (loosely)
Patination
Deliberately colouring metal with chemicals or heat so it has a controlled aged look. It can be sealed (fixed) or left to continue changing (living).
Also called: artificial patina, chemical colouring, antiquing
Perforated metal
Sheet punched or cut with holes. Open area is the percentage of the sheet that is void; for round holes in a 60-degree staggered pattern it is about 90.7 times the diameter squared divided by the pitch squared.
Also called: open area, perforated sheet
Pickling
Treating stainless or steel with acid to remove oxide, weld heat tint or scale. On stainless it takes off a thin layer of the surface, unlike passivation.
Also called: acid pickling, pickle paste
Pitting corrosion
Small, deep local corrosion spots, typically on stainless steel in salty or chloride-rich conditions. A rougher surface and trapped deposits make it more likely.
Also called: pitting
Powder coating
A dry powder sprayed onto metal and cured in an oven into a continuous paint-like film. It suits parts that fit the oven and gives a wide colour and gloss range.
Also called: powder paint, polyester powder
PRE (pitting resistance equivalent)
A number calculated from chromium, molybdenum and nitrogen content that ranks how well a stainless grade resists pitting. A higher number means better resistance, but it does not account for finish, crevices or cleaning.
Also called: PREN
Press-brake folding
Forming sheet along straight lines with a press and tooling. Minimum bend radius depends on metal and thickness, and the sheet springs back slightly.
Also called: bending, folding
PVD (physical vapour deposition)
A very thin, hard coloured coating deposited on metal in a vacuum chamber. It is typically fractions of a micron to a couple of microns thick, cannot be repaired locally, and reproduces the surface beneath it.
Also called: titanium nitride coating, PVD brass, PVD colour
Q
Qualicoat
An industry quality scheme for coatings on architectural aluminium. It adds production testing and approved materials on top of the basic European standard.
Also called: Qualicoat approved
R
RAL colour
A numbered colour reference widely used for powder coating and paint. It defines the hue but not the gloss, and metallic or textured versions need separate callouts.
Also called: RAL Classic, RAL 7016, RAL Design
S
Safe breakage
How glazing must fail in critical locations: a small clear opening, disintegration into small pieces, or pieces that are not sharp. It is tested to BS EN 12600 or BS 6206.
Also called: safety glass breakage
Surface roughness (Ra)
A measured average of how rough a surface is, in micrometres. Lower is smoother; IMOA treats Ra 0.5 um or less as smooth for corrosion purposes. The same named finish can have different Ra from different suppliers.
Also called: Ra value, average roughness, micron finish
T
Tea staining
A brown cosmetic stain that appears on stainless steel in coastal or polluted air, often on rougher or sheltered surfaces. Usually washable but a warning that the grade or finish is marginal.
Also called: surface discolouration of stainless
TIG welding
A slow, precise welding method with a tungsten electrode, used for visible seams and thin stainless or brass. MIG is faster and used where the weld will be hidden or dressed.
Also called: GTAW, MIG welding (different)
U
UKCA marking
The UK conformity mark. Fabricated structural steelwork delivered to a site in Great Britain must carry UKCA or CE marking against BS EN 1090-1.
Also called: CE marking (EU)
W
Weathering steel
A steel alloyed so that a stable rust-coloured skin forms outdoors and slows further corrosion. It needs wet-and-dry cycles to settle, stains neighbouring surfaces at first, and is risky in sealed or damp-trapping detail.
Also called: Corten, COR-TEN (trademark), S355J2W, S355J0WP
Weld quality level (ISO 5817)
A grading of acceptable weld imperfections from stricter (B) to looser (D). It is about defects, not about how a weld looks.
Also called: B, C, D quality levels