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PARALLELISM
ORIENTATIONControls how parallel a surface or axis is to a datum
⚠ DATUM REQUIREDASME Y14.5-2018 §10.7
Parallelism controls how much a surface, line, or axis can deviate from being perfectly parallel to a datum plane or axis. The tolerance zone is two planes (for surface parallelism) or a cylinder (for axis parallelism with ⌀) parallel to the datum at the specified tolerance apart.
WHEN TO USE IT
Use parallelism when two surfaces or axes must be parallel for function — such as mating faces, guide rails, or shaft-to-shaft relationships. Always requires a datum reference to define what the feature must be parallel to.
COMMON MISTAKES
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Omitting the datum reference — parallelism always requires at least one datum✕
Confusing parallelism with flatness — flatness has no datum, parallelism always does✕
Forgetting the ⌀ symbol when controlling an axis rather than a surface✕
Using parallelism when the intent is to control both orientation and location — use position insteadIS YOUR CALLOUT CORRECT?
Check these before releasing your drawing.
Does the FCF include at least one datum reference?
Parallelism always requires a datum. Without it, use flatness instead.
If controlling an axis, does the FCF include the ⌀ symbol?
Axis parallelism uses a cylindrical tolerance zone and requires the ⌀ symbol.
Is the datum feature established on the drawing with a datum feature symbol?
Every datum referenced in an FCF must be identified on the drawing.
OTHER ORIENTATION CONTROLS
Redprint checks parallelism automatically
Redprint checks that parallelism FCFs include a valid datum reference and flags missing ⌀ symbols on axis parallelism callouts.