Stock forms, types and sizes (AQA GCSE Design and Technology): Revision Notes
📚Revision Notes
Stock forms, types and sizes
Introduction to stock forms
Metal stock forms are pre-manufactured metal shapes that are commercially available in standard sizes and cross-sections. These ready-made forms are incredibly useful because they save significant time during the manufacturing process and make it much easier to incorporate metal components into your designs. Instead of having to machine or form metal from scratch, you can select the appropriate stock form that closely matches your requirements.
Note
Stock forms are the foundation of efficient metalworking. By using these standardised components, you can focus your time and energy on the unique aspects of your project rather than creating basic shapes from raw materials.
Types of metal stock forms
Metal bars and rods
Metal bars and rods feature a solid cross-section throughout their length, making them strong and versatile for many applications. These come in several different cross-sectional shapes to suit various engineering and design needs:
- Square bars - provide flat surfaces for mounting and joining
- Round bars - ideal for shafts, pins, and rotating components
- Half-round sections - useful for decorative edges and specialised applications
- Hexagonal bars - offer multiple flat surfaces and resist rotation
- Flat bars - perfect for brackets, supports, and structural elements
- Angle sections - excellent for corner reinforcement and framework construction
Metal tubes and pipes
Unlike solid bars, metal tubes and pipes have a hollow cross-section, which makes them lighter while still maintaining good strength properties. The hollow design also allows for the passage of cables, fluids, or other materials. These are manufactured in various cross-sectional shapes:
- Rectangular tubes - commonly used in structural framework
- Hexagonal tubes - specialised applications requiring specific geometry
- Round tubes - ideal for plumbing, structural supports, and aesthetic applications
- Square tubes - perfect for framework and mounting systems where flat surfaces are needed
Metal sheets
Metal sheets are flat, thin pieces of metal that come in a range of thicknesses, typically from 0.6mm to 3mm. These sheets are incredibly versatile and can be cut, bent, formed, and shaped into numerous components. They're commonly used for panels, covers, brackets, and decorative elements.
Note
The versatility of metal sheets makes them one of the most commonly used stock forms in both professional and educational metalworking projects. Their ability to be formed into complex shapes while maintaining structural integrity is particularly valuable.
Measurement and sizing systems
Understanding how metal stock forms are measured is crucial for selecting the right material for your project. There are several key measurement parameters you need to know.
Available sizes and dimensions
Metal stock forms are measured using length, width, and various other dimensional parameters depending on the specific type of material.
Important
Gauge system: This refers to the thickness of the metal, but it works in reverse to what you might expect - thinner metals actually have higher gauge numbers. This inverse relationship is important to remember when selecting materials.
Important
Key Measurement Definitions:
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Cross-sectional area: Found by cutting through the metal perpendicular to its length and measuring the solid area of that cut surface. This is particularly important for calculating strength and load-bearing capacity.
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Diameter: For round bars and tubes, this is the measurement taken across the widest point of the circular cross-section.
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Wall thickness: For tubes and pipes, this represents how thick the metal walls are, calculated by subtracting the internal diameter from the external diameter.
Metal fixings and fasteners
Metal fixings are essential hardware components used to join, connect, and assemble metal parts together. Understanding the different types and their applications is crucial for successful metalworking projects.
Bolts and basic nuts
Bolts typically feature a hexagonal head design and are designed to work together with nuts to create strong, removable connections. The hexagonal head allows you to apply significant torque using standard tools like spanners or socket wrenches.
Specialised nuts
Nyloc nuts: These innovative fasteners include a polymer insert (usually coloured) that helps resist the nut from working loose due to vibration or repeated stress. However, they do have some limitations - they require tools to attach properly and may take longer to install than standard nuts.
Important
Critical Information about Nyloc Nuts: Nyloc nuts are designed for single use only, as the polymer insert becomes less effective if used multiple times. Always use a fresh nyloc nut when reassembling components.
Wing nuts: These feature hand-tightenable extensions that allow you to assemble and disassemble connections without tools. This makes them excellent for applications where frequent adjustment or removal is needed.
Machine screws and washers
Machine screws have parallel threads and come in a variety of drive systems and head shapes to suit different applications and aesthetic requirements. The choice of head type affects both the tool needed and the final appearance of the assembly.
Washers serve two important functions: they spread the load over a larger area to prevent damage to the surface material, and spring washers specifically help resist loosening by maintaining tension in the connection.
Rivets
Pop rivets: These are permanent fasteners used for joining metal sheets together. A special rivet gun is required for installation, but the major advantage is that you only need access to one side of the work piece during installation.
Snap rivets: Another type of permanent fastener for metal sheet joining, but these require specialised snap tools and need access to both sides of the work piece during installation.
Note
The choice between pop rivets and snap rivets often comes down to accessibility. If you can only reach one side of your workpiece, pop rivets are the better choice. If you have access to both sides, snap rivets may provide a cleaner finish.
Thread specifications
When working with threaded fasteners, understanding thread measurements is essential for proper fit and function.
Example
Thread Measurement Example:
Pitch: This refers to the distance a nut or bolt would travel if wound one complete revolution on a screw thread. For example, a thread with 1.5mm pitch means the fastener advances 1.5mm for each complete turn.
Diameter: This is the outer measurement of the thread. For example, M12 indicates a metric thread with a 12mm outer diameter.
Practical applications
Understanding stock forms, their sizes, and appropriate fixings allows you to:
- Select the most efficient material for your project
- Minimise waste and machining time
- Ensure proper strength and durability in your designs
- Choose appropriate joining methods for different applications
- Calculate material requirements accurately
Summary
Key Points to Remember:
- Stock forms save time - Using pre-manufactured shapes reduces machining and forming work
- Gauge numbers work backwards - Higher gauge numbers mean thinner metal thickness
- Choose fixings carefully - Consider whether you need permanent (rivets) or removable (bolts/nuts) connections
- Nyloc nuts are single-use - The polymer insert becomes less effective after repeated use
- Wall thickness matters - For tubes, calculate this by subtracting internal from external diameter