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Use the free state symbol for your plastic, sheet metal and other flexible parts. One of the Fundamental Rules in the Standards is that all dimensions and tolerances apply in the free state condition unless otherwise specified. The default, then, is that all parts are considered rigid unless there is some indication that the part may be flexed or distorted for inspection. A way to indicate that a part is not rigid is to add a restraint note. If some tolerances are to be checked with the part not restrained, the free state symbol may be added to specific tolerances. Many useable sheet metal and plastic parts will pass inspection and be functional if clamped to a condition that simulates the assembled or functional state. Usually when a restraint note is applied to a drawing, at least one tolerance should be inspected in the free state to limit the free state variation. In this example the entire part is inspected with the part restrained except for the flatness spec which would be checked unrestrained in the free state. A free state symbol may only be applied if there is one or more restraint notes on the drawing.
NOTE: This drawing indicates it is in accordance with the ASMEY14.5-2018 standard, but this could be replaced with Y14.5M-1994 or Y14.5-2009
This tip is in accordance with ASME Y14.5M-1994, ASME Y14.5-2009 and ASME Y14.5-2018.
This tip was originally released in January 1999.