How should reference characters be used in patent drawings and descriptions?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

Reference characters in patent drawings and descriptions play a crucial role in clearly illustrating and explaining the invention. According to MPEP 608.01(g), there are specific rules for using reference characters:

“The reference characters must be properly applied, no single reference character being used for two different parts or for a given part and a modification of such part. See 37 CFR 1.84(p).”

Here are the key points to remember:

• Each unique part of the invention should have its own reference character.
• Do not use the same reference character for different parts.
• Do not use different reference characters for the same part.
• Reference characters in the drawings should match those used in the description.
• Every feature specified in the claims must be illustrated.
• Avoid superfluous illustrations that don’t correspond to claimed features.

Proper use of reference characters ensures clarity and consistency between your drawings and written description, which is essential for a comprehensive and easily understood patent application.