Stock Forms, Types & Sizes
GCSE — 2.1.2 In-depth Knowledge: Product Design
Stock forms for metals
Metals are available in a number of common forms, usually in standard thicknesses, lengths or diameters:
- Round rods
- Square rods
- Hexagonal rods
- Strips
- Sheets
- Round tubes
- Square tubes
- Angle and channel
Stock forms of timber
Natural timber is available in:
- Different sectional forms (plank, board, strip, square, dowel)
- Various standard sizes (lengths)
- Sawn or planed finish
- PSE (planed with squared edge)
- A range of shaped mouldings (e.g. Torus skirting board)
Manufactured boards
Manufactured boards are available in sheet form in standard sizes and thicknesses:
| Board | Standard thickness |
|---|---|
| MDF | 4, 6, 9, 12, 15, 18, 22, 25mm |
| Plywood | 4, 6, 9, 12, 15, 18, 24mm |
| Hardboard | 3.2mm |
Standard sheet size: 2440mm × 1220mm (or half size: 1220mm × 610mm)
Polymers
Polymers come in a range of standard stock forms:
- Sheets, rods, tubes — standard stock sizes
- Granules, pellets and powder — melted and formed into shapes
- Foam — blown into shape
- Film — heated and rolled
Papers and boards
Papers and boards are generally available by the sheet, roll, or ply:
- Sheets come in standard sizes — A0 is largest, halving in size each time down to A10
- Weight measured in gsm (grams per square metre)
- Board thickness measured in microns
- Ply refers to the number of layers
Knock down (KD) fittings
Standard components used to assemble products come in standard forms and sizes:
- Screws, nails, nuts and bolts
- Hinges and handles
- Cam lock fittings
- Corner blocks and brackets
- Scan fittings
- Dowels
Paper and board fittings
Standard components used with papers and boards:
- Drawing pins
- Velcro (pads/dots) for mounting
- Treasury tags
- Staples and fasteners
- Book bindings
Calculating costs
When estimating costs, designers and manufacturers must consider:
- The design and features included in the product
- The processes used to manufacture the product
- Material costs, fixtures, fittings and finishes required
- Energy, labour, machinery and intellectual property costs
Calculating quantities and costs
Worked example 1 — parts from a sheet
A product needs rectangular MDF parts 200 mm × 150 mm. A half sheet measures 1220 mm × 610 mm and costs £12.00.
- Along the length: 1220 ÷ 200 = 6.1 → 6 parts (always round down)
- Along the width: 610 ÷ 150 = 4.07 → 4 parts
- Parts per sheet: 6 × 4 = 24
- Cost per part: £12.00 ÷ 24 = £0.50
Worked example 2 — lengths from timber
Pieces 350 mm long are cut from a 2400 mm length of pine. Each saw cut removes 3 mm (the kerf).
- Length used per piece: 350 + 3 = 353 mm
- 2400 ÷ 353 = 6.8 → 6 pieces
- Waste: 2400 − (6 × 353) = 282 mm
Worked example 3 — total cost of a prototype
| Item | Quantity | Unit cost | Total |
|---|---|---|---|
| Acrylic sheet (300 × 200 mm) | 1 | £3.20 | £3.20 |
| M4 bolts and nuts | 4 | £0.15 | £0.60 |
| Hinges | 2 | £0.85 | £1.70 |
| Spray paint | 0.25 can | £6.00 | £1.50 |
| Total material cost | £7.00 |
Remember that the true cost of a product also includes labour, energy, machine time, packaging and profit.
Always show your working, include units, and round down when working out how many parts fit — you cannot use part of a part.