Projected Tolerance Zone (Ⓟ)

The Ⓟ modifier that projects the zone above a threaded hole, to control the fastener itself.

Definition

The projected tolerance zone (Ⓟ) extends the tolerance zone beyond the feature itself — most commonly above a threaded or press-fit hole, to the height the mating fastener will project. The zone starts at the surface and runs out to a specified height H, and the fastener must lie within it over that entire height, not just where the hole is. The symbol sits in the tolerance compartment after the tolerance value, with the projected height following it: ⌖ ⌀0.2 Ⓟ 10 A B.

Why the zone needs projecting

A position tolerance on a threaded hole controls the hole's location at the surface of the part — but the stud or bolt projecting from that hole can lean, and a small angular error grows with distance. The mating part clears the fastener over its whole thickness, not at the hole mouth, so the tolerance that matters is the fastener's location at the top of the projection. A surface-only callout can pass a leaning stud that jams the assembly; the projected zone states the requirement where the function actually happens.

Reading a feature control frame

⌖ ⌀0.2 Ⓟ 10 A B reads as a position tolerance of 0.2 diameter, projected 10 beyond the surface, located from datums A and B. The Ⓟ and the height both live in the tolerance compartment, after the value. The zone is oriented and located from the datums exactly like an ordinary position zone — the projection only changes where it applies, not how it is anchored.

When to use it

• Threaded holes for bolted assemblies where the bolt projects into a mating part — the classic case
• Press-fit studs and posts that must clear a cover plate or second part above
• Any stack-up where the fastener's far end, not the hole mouth, is the functional point
• Not for short projections or thin mating parts where the surface tolerance already dominates — the added inspection cost buys nothing

Measurement

Functional gauge with an extended pin — a pin longer than the projected height, threaded or pressed into the hole; the part passes when the pin clears the gauge over its full projection. The classic high-volume check.

CMM at the projected height — measure the hole axis at the surface, extend it to H above, and evaluate the axis against the zone at that height. Accurate, and it reports how the error breaks down between translation and lean.

Indicator setups — with the part mounted to its datums, an indicator at height H reads the fastener or a tight-fitting plug as the part rotates; FIM stays within the zone diameter.