↔ — Restricted portion of a feature
Restricted portion of a feature · Modificadores de zona · ISO 1101
Example in plan
How to interpret it
On the drawing, “— 0.02 applied only between two shoulder faces” states a restricted portion of a feature requirement.
What controls
Limits the scope of the tolerance to a specific portion of the feature instead of its full extent. The portion is indicated on the drawing with a thick chain line next to the surface, located with basic dimensions, or with letters marking its ends. Outside that portion, that tolerance simply does not apply, even though the surface continues: whatever is there is governed by other dimensions or by the drawing's general tolerances. It is the clean way to ask for precision where it is really needed (a bearing seat, the guided portion of a rod, the usable threaded length) without driving up the cost of the rest of the part. What it does NOT mean is that the rest is free of all control, or that the portion can be chosen on the shop floor: the drawing sets the zone.
How to verify
When programming the CMM or sweeping with a dial indicator, limit the travel to the indicated zone and discard the points outside it: if they are included, deviations the drawing does not control are picked up and the part is rejected for no reason. Reference the ends of the portion from the same datum reference frame the drawing uses, not by eye from the end of the part. It is also advisable to leave a small margin at the ends so as not to capture fillet radii, tool entry marks or burrs, and to note the evaluated portion in the report.
Common mistakes when interpreting it
- Measuring the full length of the feature instead of the indicated portion, picking up deviations the drawing does not control.
- Assuming the rest of the feature has no requirement: it is still subject to the other dimensions and to the general tolerances.
- Choosing the portion on the shop floor at your own discretion when the drawing locates it with basic dimensions.
How to get it in the workshop / if it comes out of tolerance
Common on rods with a collar: straightness or runout only between two faces. Mark the portion with a line and the ↔ symbol. Make use of it when planning: you can rough the rest and save the finishing pass, grinding or honing for the specified portion, which saves time and tool wear. Physically mark the ends of the portion with a marker or scriber before measuring, so the inspector does not sweep too much or too little.
If the restricted portion fails, work that portion like any other form or runout problem: support with a steady rest if it is slender, a light finishing pass and a sharp cutting edge. If the failure appears right at the ends, it is usually tool entry or exit: move the start of the cut outside the controlled zone. And if the rejection comes from a measurement that swept the whole part, correct the inspection program before touching the machine, because the problem is in the method.
Related symbols
Other symbols in Zone modifiers
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