Unequally disposed profile places the tolerance zone unevenly about the true profile. The total tolerance still defines the full zone width. In the ASME example below, the value after Ⓤ specifies the portion outside the material; the rest lies inside. Use it when variation is more acceptable in one direction than the other.
Datum required
Optional
MMC / LMC applicable
Usually not applicable — profile control
Control type
Profile
What it controls
The profile zone is offset from the true contour rather than equally disposed about it.
Typical features
Cast blanks, forgings and surfaces with deliberately asymmetric stock allowance.
INTERACTIVE APPLICATION
GD&T unequally disposed profile example: cast face with machining stock
EQUALLY DISPOSED PROFILE
The zone is centred on the true profile
Total profile tolerance: 0.30.
Equal allocation: 0.15 outside and 0.15 inside the material.
Limitations
Normal surface profile already controls the full 3D face.
Equal allocation cannot reserve a larger share on one side.
UNEQUALLY DISPOSED PROFILE
More of the zone lies outside the material
Total profile tolerance: 0.30.
Ⓤ0.2 allocates 0.2 outside and the remaining 0.1 inside.
Advantages
Allows more variation where extra material is acceptable.
Protects clearance or finish stock by specifying the two shares.
01 / PURPOSE
Why is Unequally disposed profile used?
Use UDP when an equally centred zone gives too much freedom on the wrong side. A casting may need extra material for machining cleanup, while a mating face may need tighter control on the side that affects assembly fit.
The first tolerance value is the full zone width. The value after Ⓤ is the share outside the material; the remainder is inside. This lets you favour one direction without changing the total tolerance. Coated parts can also use a deliberate allocation to manage added thickness and clearance, provided the drawing states whether the requirement applies before or after coating.
02 / APPLICATION
Where is Unequally disposed profile used?
Typical uses include castings and forgings with machining stock, coating allowances, mating surfaces where clearance matters, and faces where extra material is acceptable on one side. Choose the allocation from the final function and manufacturing process.
03 / DRAWING
How is unequally disposed profile used?
Define the true surface using basic geometry, set the total zone width, then specify how much lies outside the material. Add datum references where the design requires them.
Unequally disposed profile drawing examplecast face with machining stock
The part stays fixed. Only the zone shifts outward: 0.2 outside + 0.1 inside = 0.30 total. The Ⓤ value is the outside portion, not the shift of the zone centre.
How to read the frame
Read the surface-profile symbol, the 0.30 total tolerance, then Ⓤ and its 0.2 outside allocation. Datum A provides the stated reference. The inside portion is 0.30 − 0.2 = 0.1.
Value-by-value breakdown
04 / VALUES
Commonly defined variable values
The controlling value is a tolerance-zone width, not a universal process grade. For this unequally disposed profile example, the drawing states the controlled feature and applicable extent.
Scroll the table sideways to see every column.
Illustrative unequally disposed profile tolerances for early design discussion
Application
Illustrative starting value
Example feature
Notes / caution
Cast Face With Machining Stock
0.30 Ⓤ 0.2 mm (ASME example)
cast face with machining stock
0.2 outside, 0.1 inside; validate against function and the drawing standard.
These are planning examples, not universal rules or guaranteed process capabilities. Set the actual tolerance from function, size, length, process capability, inspection method and the standard specified on the drawing.
ASME Y14.5-2018 (R2024)
The value after circled U gives the portion of the total profile tolerance outside the material. The remaining tolerance lies inside.
