What is an envelope?

What is an envelope?

• A. The outer boundary that a part must fit within per the tolerance.
• B. A hole that is oversize
• C. A datum feature boundary
• D. A type of surface texture

Answer: (A)

An envelope is the outer boundary that a part must stay within given its tolerances. It represents the worst-case external geometry a part could have and is used to ensure that every acceptable part will still fit with mating parts in an assembly. Think of it as a virtual, maximal boundary that contains all permissible variations of the part. If a part remains inside this envelope, it will assemble properly. The other ideas describe different GD&T concepts or features (a specific hole size issue, a datum feature boundary, or a surface texture) and don’t define the envelope.

An envelope is the outer boundary that a part must stay within given its tolerances. It represents the worst-case external geometry a part could have and is used to ensure that every acceptable part will still fit with mating parts in an assembly. Think of it as a virtual, maximal boundary that contains all permissible variations of the part. If a part remains inside this envelope, it will assemble properly. The other ideas describe different GD&T concepts or features (a specific hole size issue, a datum feature boundary, or a surface texture) and don’t define the envelope.