GD&T concept · Rule

Restrained Condition Note

A text note requiring the part to be measured while restrained — held the way it will be held in service.

Definition

A restrained condition note directs the inspector to restrain the part — hold it against specified datum features or in a defined fixture, applying specified forces or fastener torques — before verifying the tolerances the note applies to. The restraint simulates how the part is actually held in service: a gasket measured clamped between flanges, a cover measured with its mounting screws torqued. The tolerances are then verified in that restrained state, because that is the state in which the part must function.

There is no symbol — and that is the point

Unlike Ⓕ, independency, or Ⓜ, the restrained condition has no standardized symbol and appears nowhere inside a feature control frame. It is a text note — typically NUMBERED NOTES on the drawing: NOTE 2: FLATNESS SHALL BE VERIFIED WHILE THE PART IS RESTRAINED TO DATUM FEATURES A AND B WITH FOUR M6 FASTENERS TORQUED TO 10 Nm. Every restraint that changes the measurement must be spelled out: which datum features, what contact sequence, what forces. Two inspectors restraining the same part differently produce different parts — so the note is only complete when another shop could reproduce the restraint exactly.

Free state vs. restrained: which state for which tolerance

The two mechanisms are complements, and drawings that need one often need both. The restrained condition note establishes the drawing-wide requirement: this part is verified restrained. The Ⓕ symbol then carves out exceptions: tolerances marked Ⓕ are verified unrestrained. A typical sheet-metal cover: hole positions verified restrained (the holes must align with the mating part's holes once bolted), while the flatness of the unsupported panel face is verified free (it is a visible surface, not a sealing one — how it lies loose is how the customer sees it).

Left: the part in its free state — no forces applied beyond gravity, drawn in its natural deflected shape; a tolerance carrying Ⓕ is verified in this state. Right: the same part restrained to datum simulators per a restrained-condition note — forced toward the shape it assumes mounted in service. The note is text (there is no standardized restrained symbol); Ⓕ exists to opt individual tolerances back out of a drawing-wide restrained requirement. Schematic, exaggerated.

When to restrain — and when not to

Parts whose function only appears once installed: gaskets, covers, bonded panels — restrain to the mounting datums and verify there
Parts so flexible that a free-state check cannot distinguish good from bad — restraint makes inspection repeatable
Parts whose function IS the free-state shape — leave them unrestrained and specify realistic free-state tolerances instead
Never restrain a feature whose tolerance carries Ⓕ — the note and the modifier must not contradict

Writing a usable note

A restrained condition note carries three things: the datum features the part is restrained to (in precedence order), the restraining method (fixture elements, fastener count and torque, clamping sequence), and the tolerances it applies to (all of them, or the listed ones). Understating any of the three turns the note into an argument at inspection. The 2018 edition of Y14.5 added explicit guidance for non-rigid parts: the restraint should simulate the functional assembly, use the datum features the function uses, and apply only the forces the installation applies.