How should reference characters be used in patent drawings?

Reference characters in patent drawings should be used according to the following guidelines from 37 CFR 1.84(p):

• Use Arabic numerals, preferably in the clockwise direction and starting with the number 1
• Use plain legible symbols and characters
• Must measure at least 0.32 cm (1/8 inch) in height
• Should not be placed upon hatched or shaded surfaces
• Must be different for different parts; the same part must be designated by the same reference character throughout the application
• Lead lines must be used to indicate the parts to which they refer and should not cross each other

Additionally, reference characters mentioned in the description must appear in the drawings, and vice versa. Characters not mentioned in the description should not appear in the drawings.

To learn more:

• reference characters
• patent drawings
• drawing labels