10.6 Modifier Rules for Profile & Combined Controls (Profile with Position, Orientation and Runout)

ASME GDTP Technologist Y14.5-2009

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1 Chapter 1: Scope, Certification Logistics, Fundamental Rules & General Dimensioning

1.1 ASME GDTP Technologist Exam Scope, Prometric Logistics, & Certification Rules 1.2 Fundamental Rules of ASME Y14.5-2009 (Rules a through p) 1.3 Engineering Drawing Standards, Drawing Units, & Basic vs. Toleranced Dimensions 1.4 Dimensioning Features: Diameters, Radii, Chamfers, Countersinks, Counterbores, Spotfaces, Keyseats & Slots 1.5 Application of Dimensions & Location of Features: Lines, Leaders, Reference Dimensions, Rectangular vs. Polar Coordinates

2 Chapter 2: Features, Limits of Size, & Material Condition Principles

2.1 Features, Features of Size, & Limits of Size 2.2 Rule #1 (Taylor Principle / Envelope Rule), Its Exceptions & Overrides 2.3 Material Condition Concepts: MMC, LMC, & RFS Calculations

3 Chapter 3: General Tolerancing & Symbology

3.1 Direct Tolerancing, Limit Dimensioning, & Angular Tolerancing 3.2 The 14 Geometric Characteristic Symbols, Feature Control Frames, & Special Modifiers 3.3 Screw Threads, Gears & Splines, Angular Surfaces, Tapers & Statistical Tolerancing 3.4 Feature Control Frame Placement, Combined Frames, Tolerance Zone Definition & Tabulated Tolerances

4 Chapter 4: Datum Reference Frames & Degrees of Freedom

4.1 Theoretical Datums, Datum Feature Simulators, & Physical Datum Features 4.2 Degrees of Freedom Constraint & The 3-2-1 Datum Precedence System 4.3 Planar, Cylindrical, & Width Datum Feature Establishment

5 Chapter 5: Advanced Datum Applications: Targets, Boundary Modifiers, Customized Frames & Restrained Condition

5.1 Datum Target Points, Lines, Areas, & Movable Datum Simulators 5.2 Material Boundary Modifiers (RMB, MMB, LMB) & Datum Shift Calculations 5.3 Functional Datum Feature Selection, Multiple Datum Reference Frames & Simultaneous vs. Separate Requirements 5.4 Rotational Constraint About a Datum Axis or Point & Customized Datum Reference Frames 5.5 Irregular & Complex Datum Features, Mathematically Defined Surfaces, Restrained Condition & Datum Feature Controls

6 Chapter 6: Form Tolerances

6.1 Flatness & Straightness Controls for Surfaces & Features of Size 6.2 Circularity & Cylindricity Controls, Differences, & Inspection

7 Chapter 7: Orientation Tolerances

7.1 Parallelism Controls for Planar Surfaces & Cylindrical Features of Size 7.2 Perpendicularity & Angularity Tolerances with Basic Angles & Tangent Plane

8 Chapter 8: Location: Position Fundamentals & Calculations

8.1 Position Tolerancing Fundamentals, True Position, & Coordinate Conversions 8.2 Bonus Tolerance & Virtual Condition Calculations for Internal & External Features 8.3 Projected Tolerance Zones (Ⓟ Modifier) & Fixed vs. Floating Fastener Formulas 8.4 Zero Positional and Orientation Tolerancing at MMC and at LMC 8.5 Surface vs. Axis Interpretation of Position & the Boundary Concept for Slots, Tabs & Noncircular Features

9 Chapter 9: Location: Patterns, Composite Controls, Coaxial & Symmetrical Relationships, and Functional Gaging

9.1 Hole & Slot Patterns, Multi-Segment Frames, & Composite Position Tolerancing 9.2 Functional Gaging Principles & Inspection Verification of Position 9.3 Coaxial Holes, Counterbored Holes, Non-Parallel Axes, Spherical Features & Bidirectional Position 9.4 Concentricity & Symmetry Tolerances Under ASME Y14.5-2009 9.5 LMC Applied to Position: Wall Thickness, Breakout Protection & Boundary Calculations

10 Chapter 10: Profile Tolerances

10.1 Profile of a Line & Profile of a Surface Fundamentals & Basic Geometry 10.2 Bilateral, Unilateral, & Unequally Disposed Profile Boundaries (Ⓤ Modifier) 10.3 Composite Profile Tolerances vs. Multiple Single-Segment Profile Controls 10.4 Profile Verification, Coplanarity Controls, & Non-Rigid Parts 10.5 Profile Applications: Conicity, Extruded and Irregular Shapes, and Profile-Controlled Datum Features 10.6 Modifier Rules for Profile & Combined Controls (Profile with Position, Orientation and Runout)

11 Chapter 11: Runout Tolerances & Comparative Control Analysis

11.1 Circular Runout vs. Total Runout Interpretation & Dial Indicator Verification 11.2 Comparative Analysis: Runout vs. Form, Orientation, & Concentricity Controls

10.6 Modifier Rules for Profile & Combined Controls (Profile with Position, Orientation and Runout)

Key Takeaways Explain This Topic AI

ASME Y14.5-2009 para. 8.5 states that because profile is primarily a surface control, regardless of feature size is the default condition on a size feature application and MMB or LMB modifiers are permissible only on the datum feature references.

Material condition modifiers may never be attached to a profile tolerance value, but material boundary modifiers on a datum feature reference in a profile frame do permit datum feature shift.

The unequally disposed profile modifier is legal in the tolerance compartment because it redistributes the stated tolerance about the true profile rather than creating bonus tolerance.

Para. 8.8 permits profile to be combined with positional tolerancing to control the boundary of a noncylindrical feature, with basic dimensions and the profile tolerance controlling shape and size while the positional tolerance establishes a theoretical boundary shaped identically to the true profile.

In a refinement stack each successive control must carry a smaller tolerance value than the control it refines and constrain fewer degrees of freedom; a refining control with a larger value adds no control at all.

Last updated: September 2026

10.6 Modifier Rules for Profile & Combined Controls (Profile with Position, Orientation and Runout)

Quick Answer: Para. 8.5 states the modifier rule that decides a surprising number of exam items: since profile control is used primarily as a surface control, "regardless of feature size" is the default condition on a size feature application, and MMB and LMB application (modifiers) is only permissible on the datum feature references. In other words, Ⓜ and Ⓛ may never be attached to a profile tolerance value , but Ⓜ and Ⓛ may be attached to the datum feature letters in a profile frame. Para. 8.8 then permits profile to be combined with other types of geometric tolerancing — most importantly with position, to control the boundary of a noncylindrical feature , where the basic dimensions and profile tolerance establish the zone controlling shape and size , while the positional tolerance establishes a theoretical boundary shaped identically to the true profile .

The Modifier Rule (Para. 8.5) ┌───┬──────────────┬──────────┬──────────┬───┐
│ ⌓ │ 0.4 │ A │ B Ⓜ │ C │
└───┴──────┬───────┴────┬─────┴─────┬────┴───┘
│ │ │
Ⓜ / Ⓛ NEVER │ └───────────┴── Ⓜ (MMB) and Ⓛ (LMB)
permitted here ARE permitted here
(RFS is the default and (on the DATUM FEATURE
the only condition) REFERENCES)

The reasoning behind the asymmetry is worth internalizing, because it makes the rule impossible to forget:

A profile tolerance controls a surface. A surface has no MMC and no LMC — those are properties of a feature of size . There is no departure from a material condition to convert into bonus tolerance, so a bonus mechanism on the tolerance value would be meaningless.

A datum feature reference in a profile frame may still be a feature of size , and that feature of size does have an MMB and an LMB. Referencing it at MMB permits datum feature shift exactly as it would in a position frame.

Element of a Profile Frame Ⓜ / Ⓛ Permitted? Effect if Permitted
The profile tolerance value No — RFS is the default and the only condition —

A datum feature reference to a feature of size Yes (MMB / LMB) Datum feature shift as the datum feature departs from its boundary

A datum feature reference to a planar surface No A plane has no material boundary

The one-line exam answer: profile takes no material condition modifier on the tolerance; it takes material boundary modifiers only on datum feature references. Any option offering ⌓ | 0.4 Ⓜ | A | B | C is wrong on its face.

Distinguish From the Ⓤ Modifier

The unequally disposed profile modifier Ⓤ (para. 8.3.1.2) is legal in the tolerance compartment, and candidates sometimes conflate the two rules. Ⓤ does not create bonus tolerance — it redistributes the stated tolerance about the true profile. ⌓ | 0.6 Ⓤ 0.2 | A is a legal frame; ⌓ | 0.6 Ⓜ | A is not.

Combined Controls (Para. 8.8)

Profile tolerancing may be combined with other types of geometric tolerancing. Profile tolerancing may be combined with positional tolerancing where it is necessary to control the boundary of a noncylindrical feature. In such an example the basic dimensions and the profile tolerance establish a tolerance zone to control the shape and size of the feature . Additionally, the positional tolerance establishes a theoretical boundary shaped identically to the true profile . For an internal feature, the surface may not encroach inside that boundary; for an external feature, it may not extend outside it.

Why Two Controls Are Needed

Consider a D-shaped hole that must receive a D-shaped shaft.

Requirement Control That Delivers It Why the Other One Cannot

The opening must be the right shape and size Profile of a surface with basic dimensions Position controls location, not contour

The opening must clear the mating shaft wherever it lands Position , establishing a boundary of the true profile shape Profile alone would allow the whole correct-shaped opening to sit off location

This is exactly the mechanism para. 7.4.5 pointed to when it noted that the boundary concept can be applied to irregularly shaped features of size, such as a D-shaped hole with a flattened side, where the center is not conveniently identifiable — and cross-referenced para. 8.8 for the details. D-SHAPED HOLE: PROFILE + POSITION (para. 8.8)

╭──────────────────────╮
│ ┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈ │ ← positional boundary: same SHAPE as the

│ ┈╭──────────────╮┈ │ true profile, located at true position.

│ ┈│ │┈ │ Internal feature: surface may not

│ ┈│ D-shaped │┈ │ encroach INSIDE this boundary.

│ ┈│ opening │┈ │
│ ┈╰──────────────╯┈ │ ← profile zone: controls SHAPE and SIZE

│ ┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈ │ of the contour itself.

╰──────────────────────╯
Other Combinations Para. 8.8 Authorizes

Profile + orientation : a profile tolerance locating a contoured face, refined by a perpendicularity or angularity tolerance that constrains only its tilt. Recall the hierarchy — the refining control must be tighter than the control it refines.

Profile + runout : profile defining a contoured surface of revolution, with a circular or total runout tolerance refining its behaviour about the datum axis.

Profile + form : a flatness tolerance refining a nominally planar portion of a profiled surface.

Composite profile (para. 8.6) and multiple single-segment profile (para. 8.7) are the two-tier constructions of profile itself, and should not be confused with combining profile with a different characteristic under 8.8.

The Refinement Hierarchy in Practice

Tier Control Typical Value What It Constrains
1 ⌓ 0.8 | A | B | C 0.8 Location, orientation, form, size of the contour
2 ⌓ 0.3 | A 0.3 Orientation and form, free to translate
3 ⟂ 0.1 | A 0.1 Tilt only
4 ⏥ 0.05 0.05 Form of a planar portion only

Each tier is tighter than the one above it and constrains fewer degrees of freedom. A refining control with a larger value than the control it refines adds nothing and is a drawing defect — a favourite exam distractor.

Reading order for any combined-control question: identify each frame's characteristic , then its datum references , then its value . If a lower frame has fewer datums and a smaller value, it is a legitimate refinement. If it has fewer datums and a larger value, it controls nothing.