Short Answer:
In an engineering drawing, fasteners like nuts, bolts, and screws are shown using standard symbols, simplified shapes, or full detailed views. Their type, size, thread details, and position are clearly marked to help in selecting and assembling the correct fastener. Depending on the complexity, fasteners may be shown using section views or exploded views for better understanding.
To represent fasteners correctly, standard conventions such as hidden lines for threads, cross-hatching for section cuts, and note callouts for bolt sizes (like M10, M12, etc.) are followed. This ensures that anyone reading the drawing can easily understand which fasteners are used and how they fit into the assembly.
Detailed Explanation:
Representation of Fasteners in Engineering Drawing
Fasteners are essential in mechanical design because they join different parts together securely. Common fasteners include bolts, screws, nuts, washers, rivets, and pins. To ensure accurate production and assembly, these fasteners must be clearly and correctly represented in engineering drawings.
Engineers follow specific rules and drawing standards (like ISO and BIS) to show these fasteners in a way that is easy to understand, standardized, and unambiguous.
- Types of Representation
There are mainly two ways to show fasteners in a drawing:
- Simplified Representation: Used to save time and space. Only the outline shape is shown without full threads.
- Detailed Representation: Shows the threads, chamfers, slots, and full shape of the fastener. Used when detailed information is required for manufacturing or inspection.
The choice between these depends on the purpose of the drawing—assembly, manufacturing, or reference.
- Symbols and Standards
To avoid confusion, engineers use standard notations and symbols to represent fasteners. These are based on international or national standards like:
- ISO (International Organization for Standardization)
- DIN (German standard)
- BIS (Bureau of Indian Standards)
- ANSI (American standard)
For example:
- A hex bolt of 10 mm diameter and 30 mm length is written as M10 × 30
- Thread type may be added: M10 × 1.5 (where 1.5 is the pitch)
- Representation in Views
Fasteners can appear in several views in a drawing:
- Front View / Top View: Shows the overall shape and head type (hex, round, slot).
- Section View: Helps to show the internal connection of the nut and bolt.
- The bolt shaft is shown as a solid circle or rectangle.
- The nut and threaded hole are shown using cross-hatching or hidden lines for threads.
Hidden Lines: Used to represent threads that are not visible from the outside.
Thread Lines: In detailed views, threads are shown using thin parallel lines inside the bolt or screw.
- Notes and Callouts
Drawings often include notes or leader lines pointing to fasteners, mentioning:
- Size (e.g., M8, M12)
- Length (e.g., ×30 mm)
- Thread type (e.g., coarse, fine)
- Material (e.g., steel, brass)
- Coating (e.g., zinc plated)
Example:
M8 × 40, Hex Bolt, Steel, Zinc Coated
This note helps the purchasing team or assembly worker to select the exact fastener without confusion.
- Common Fasteners in Drawings
- Hex bolts and nuts: Most common; shown with a hexagonal shape in top view.
- Screws: Can be represented with or without head slots depending on type.
- Washers: Shown as flat rings between nut/bolt and the surface.
- Threaded holes: Represented using broken circles or dashed lines.
- Thread Representation
- External Thread (bolt): Shown with continuous and dashed lines around the shaft.
- Internal Thread (nut or hole): Shown with two concentric circles in end view, or dashed lines in section view.
In simplified drawings, threads may be replaced with standard labels like “M10 tapped hole”.
- Exploded Views and Assemblies
In assembly or exploded views, fasteners are shown in their correct positions, often separated to show how parts fit together. Balloons or reference numbers link them to a parts list (BOM).
This helps users understand:
- Where each fastener goes
- In what sequence they should be assembled
- What sizes are needed
Conclusion
Fasteners like bolts, nuts, and screws are represented in engineering drawings using standardized symbols, views, and notations. Depending on the need, they may be shown in simplified or detailed forms. Key elements like size, thread, type, and position must be clearly mentioned using proper notes or callouts. Correct representation of fasteners ensures smooth manufacturing, error-free assembly, and proper communication between designers, machinists, and technicians.