Stock Forms and Standard Components
Stock Forms and Standard Components
Understanding how materials are supplied and the role of standard (bought-in) components is essential for AQA GCSE D&T. This topic covers how designers specify materials and use off-the-shelf parts to save time, cost, and ensure reliability.
Stock Forms
Stock forms are the standard shapes and sizes in which materials are commercially available. Using standard stock forms reduces waste and cost because they are mass-produced and readily available.
Timber stock forms:
| Form | Description | Typical Use |
|---|---|---|
| Plank | Wide, flat sawn timber (over 50mm wide) | Shelving, table tops, cladding |
| Board | Sheet material (plywood, MDF, chipboard) — typically 2440 × 1220mm | Furniture carcasses, construction panels |
| Strip | Narrow rectangular section | Edging, small frames |
| Square section | Equal width and height | Table legs, structural framing |
| Dowel | Cylindrical rod | Joints, handles, model making |
| Moulding | Shaped profile (e.g. skirting board, dado rail) | Decorative trim |
Metal stock forms:
| Form | Description | Typical Use |
|---|---|---|
| Sheet | Flat, thin (up to ~3mm) | Car body panels, enclosures |
| Plate | Flat, thicker (over 3mm) | Structural, machine bases |
| Round bar / rod | Solid circular cross-section | Shafts, axles, machining |
| Square / rectangular bar | Solid square/rectangular section | Frames, brackets |
| Tube (round, square) | Hollow section | Bicycle frames, furniture |
| Angle | L-shaped cross-section | Structural brackets, shelving supports |
| I-beam / H-beam | I or H cross-section | Construction (high strength-to-weight) |
| Wire | Thin, flexible, drawn from rod | Springs, electrical connections, jewellery |
| Hexagonal bar | Six-sided cross-section | Nuts, bolts (machining blanks) |
Polymer stock forms:
| Form | Description | Typical Use |
|---|---|---|
| Sheet | Flat panels (e.g. acrylic, polypropylene) | Display cases, vacuum forming |
| Rod | Solid circular section | Machining on a lathe |
| Tube | Hollow circular section | Plumbing, cable conduit |
| Film | Very thin, flexible sheet | Packaging, laminating |
| Granules / pellets | Small pieces for melting | Injection moulding, extrusion |
| Foam (expanded) | Lightweight, cellular structure | Packaging, insulation |
| Powder | Fine particles | SLS 3D printing, rotational moulding |
Textile stock forms:
- Woven fabric — structured, stable (plain/twill/satin weave)
- Knitted fabric — stretchy, flexible
- Non-woven fabric (e.g. felt) — fibres bonded by heat/adhesive, no grain
- Yarn/thread — for sewing, knitting, weaving
Paper and board stock forms:
- Sheets — A-sizes (A0–A6) or SRA sizes for bleed
- Rolls — continuous for printing and packaging lines
- Various weights measured in GSM (grams per square metre): paper < 170 GSM; card/board > 170 GSM
Standard Components
Standard components are pre-manufactured, off-the-shelf parts that designers incorporate into products rather than making from scratch. They are produced to recognised standards (e.g. ISO, BSI) ensuring consistency and interchangeability.
Advantages of standard components:
- Consistency — identical every time, ensuring reliable fit and performance
- Cost-effective — mass-produced, so cheaper than custom-making
- Availability — readily sourced from suppliers
- Interchangeable — replaceable if they wear out or break
- Quality assured — manufactured to tested standards
- Reduced assembly time — no need to fabricate from raw materials
Common standard components:
| Category | Examples |
|---|---|
| Fixings | Screws (wood, machine, self-tapping), nuts, bolts, washers, rivets, nails, staples |
| Adhesives | PVA (wood), epoxy (metals/plastics), contact adhesive (laminates), hot glue |
| Hinges | Butt hinge, piano hinge, concealed hinge |
| Catches and locks | Magnetic catch, toggle catch, cam lock |
| Bearings | Ball bearing, roller bearing, plain bearing |
| Springs | Compression, tension, torsion |
| Electronic | Resistors, LEDs, batteries, battery holders, switches, connectors, ICs |
| Gears and pulleys | Pre-made gear wheels, belt pulleys, timing belts |
| Textile | Zips, buttons, poppers, Velcro, buckles, eyelets, elastic |
Specifying Materials and Components
When specifying materials in a design, include:
1. Material type — e.g. beech hardwood, 304 stainless steel, 3mm clear acrylic
2. Stock form — e.g. sheet, round bar, dowel
3. Dimensions — length × width × thickness (mm)
4. Quantity needed
5. Finish/grade — e.g. planed all round (PAR), brushed finish, food-grade
Tolerances in Stock Forms
Manufactured stock forms have tolerances — the acceptable range of variation from the specified dimension. For example, a 20mm diameter steel rod might be specified as 20mm ± 0.1mm, meaning any rod between 19.9mm and 20.1mm is acceptable.
Tighter tolerances cost more to produce because they require more precise machinery and quality control.
Exam Tips
- You may be asked to name a suitable stock form for a given product — always explain why it is suitable (link to the product's requirements)
- Know the difference between stock forms for the same material category (e.g. sheet vs plate in metals)
- When listing standard components in a design, be specific — say "M6 countersunk machine screw" rather than just "screw"
- Standard component questions often ask for advantages — focus on consistency, cost, availability, and interchangeability
- If asked to write a cutting list or materials specification, include material, stock form, dimensions, and quantity
Key Definitions
- Stock form: The standard shape and size in which materials are commercially available from suppliers
- Standard component: A pre-manufactured part produced to a recognised standard, bought off-the-shelf rather than custom-made
- Tolerance: The acceptable range of variation from a specified dimension
- GSM: Grams per square metre — the measure of paper/card weight
- PAR (Planed All Round): Timber that has been machine-planed smooth on all four faces