Optional Modifiers (ISO)
What do the available options mean?
1. Projected Zone — Adds the
Projected Tolerance Zone symbol, Ⓟ, to indicate that the tolerance zone is projected above/outside the
workpiece surface. When you select this option, you must also enter the minimum height of the tolerance zone. When a projected tolerance zone is used, it limits the orientation deviation of the toleranced
feature of size, usually a hole, without restricting the location deviation of the hole.
2. Free State — Adds the
Free State modifier, Ⓕ, to indicate that the
geometrical tolerance applies in the unrestrained condition. This modifier is only applicable for non-rigid parts for which there is a note that indicates that tolerances are specified for the restrained state.
3. Specified Offset— Adds the Specified Offset modifier, UZ, to indicate that a profile tolerance has a specified offset. When you select this option, the value that you specify represents the offset of the theoretical profile, with the direction of the offset indicated by the sign. A "+" sign indicates "out of the material" and a "-" sign indicates “into the material”.
How do I decide which options to choose?
The Ⓟ symbol is typically used when the deviation in perpendicularity of threaded or press-fit holes could cause fasteners (i.e. screws, studs, etc.) to interfere with mating parts. In fixed fastener applications, the hole (threaded or press-fit) locates and orients the fastener. The interference can occur when the fastener is inclined with the location tolerance zone.
The Ⓕ symbol is typically used on features of
non-rigid parts. A non-rigid part is indicated by the inclusion of a
restraint note in the data set. When a restraint note is present, all dimensions are measured in the restrained state. The free state modifier is specified in
tolerance frames where the intent is to have the tolerance apply without the restraint.
The UZ modifier is used when you need to define a profile tolerance zone that is offset from the true profile of a surface. Unless there is a functional reason to offset the tolerance zone from being centered about the true profile, this modifier should not be used.