Instruction diagrams are an essential component of any product design and manufacturing process. They serve as a visual representation of how a product should be assembled, installed, or operated. However, these diagrams are not always universally understood, leading to confusion, misinterpretation, and even incorrect assembly. To prevent these issues, it's crucial to use symbols that are universally recognized and well understood.

Here are 20 universally-understood symbols commonly used in instruction diagrams:

1. Arrows – used to show the direction of movement or flow

2. Circle with an X – used to indicate a prohibited action

3. Exclamation mark – used to indicate a warning

4. Hands – used to indicate manual operation or handling

5. Lightbulb – used to indicate an idea or a suggestion

6. Padlock – used to indicate a locked or secure position

7. Rectangle with a diagonal line – used to indicate a non-functioning part

8. Recycling symbol – used to indicate recycling or environmentally-friendly actions

9. Tick mark – used to indicate a correct action or item

10. Triangle with an exclamation mark – used to indicate a hazard or danger

11. Wrench – used to indicate a tool or equipment needed

12. Zoom-in symbol – used to indicate a close-up or detailed view

13. Zoom-out symbol – used to indicate a broader or wider view

14. Plus sign – used to indicate the addition of parts or components

15. Minus sign – used to indicate the removal of parts or components

16. Screwdriver – used to indicate tightening or loosening

17. Hammer – used to indicate hammering or tapping

18. Pliers – used to indicate gripping or twisting

19. Spanner – used to indicate tightening or loosening nuts and bolts

20. Screws – used to indicate the need to screw in or out.

By incorporating these symbols into your instruction diagrams, you can help to ensure that they are clear, concise, and universally understood. By avoiding misunderstandings, you can also prevent assembly errors, save time, and reduce costs.