Question

What is the difference between bilateral and unilateral dimensions?

Answer 1

The difference between bilateral and unilateral dimensions is mainly in how tolerance (allowable variation) is applied to a given size in engineering drawings or manufacturing.

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 Unilateral Dimension:

1. Definition: Tolerance is given only in one direction (either plus or minus, not both).
   

1. Example:  
   

  \( 50^{+0.2}_{+0.0} \) mm  
  → This means the size can go up to 50.2 mm, but not below 50 mm.

1. Use Case: When we want the part to be no smaller (or no bigger) than a certain size. Often used when fitting parts together where going below/above a certain size could cause problems.
   

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 Bilateral Dimension:

1. Definition: Tolerance is given in both directions (plus and minus).
   

1. Example:  
   

  \( 50 \pm 0.2 \) mm  
  → This means the size can range from 49.8 mm to 50.2 mm.

1. Use Case: When a little variation is allowed both above and below the exact size. It's more balanced and common in general manufacturing.
   

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 Simple Analogy:

Think of making cookies with a cookie cutter:

1. Unilateral: You say, “The cookie must be at least 5 cm wide, but it can be a little wider.”  
   

1. Bilateral: You say, “The cookie can be 5 cm, but a little smaller or bigger is okay too.”
   

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Let me know if you want a visual example!