General tolerances, also known as default tolerances, title block tolerances, or Unless Otherwise Specified (UOS) tolerances, are standard tolerances for dimensional variation applied when specific tolerances aren’t explicitly stated on an engineering drawing. These tolerances provide a default level of precision, establishing acceptable ranges for part dimensions without requiring individual tolerances for each measurement.
Often found in the title block of a drawing, these tolerances cover linear and sometimes angular dimensions, with permissible variation typically based on the number of decimal places in the dimension. For instance, a dimension with two decimal places (e.g., 1.25) would have a broader tolerance than one with three decimal places (e.g., 1.250).
By specifying general tolerances, engineers and manufacturers ensure a balance between part functionality and manufacturing efficiency. These tolerances allow parts to be produced within acceptable limits while minimizing the need to define specific tolerances for each dimension, simplifying the drawing and ensuring consistency across similar parts.
See also: ISO 2768-1 and ISO 2768-2