Study guide
8.3 Bonus Tolerance at MMC and LMC
ASME GDTP Senior Level Exam
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1 Introduction & Exam Overview
1.1 Current Exam Facts 1.2 Senior Level vs Technologist and Y14.5 Revisions 1.3 How to Use This Guide and Study Strategy 1.4 The Y14.5-2018 Senior Exam and What Changed from 2009
2 Dimensioning and Symbology
2.1 Y14.5 Dimensioning Rules, Limits, and Fits 2.2 Basic Dimensions and Their Role 2.3 Feature Control Frame Structure and Reading 2.4 GD&T Symbols, Modifiers, and Communication 2.5 Screw Threads, Gears, and Splines 2.6 Angular Surfaces, Tapers, Radii, and Special Tolerance Cases
3 Datum Referencing I: Selection and Precedence
3.1 Functional Datum Feature Selection 3.2 Datum Precedence and Degrees of Freedom 3.3 Datum Targets 3.4 Datum Feature Simulators
4 Datum Referencing II: Modifiers and Shift
4.1 Multiple Datum Features and Datum Reference Frames 4.2 RMB, MMB, and LMB on Datum Features 4.3 Datum Shift Behavior 4.4 Planar vs Datum Feature of Size
5 Datum Referencing III: Setup and Calculations
5.1 Inclined and Translated Datum Features 5.2 Inspection Setup and Datum Establishment 5.3 Datum Calculation Walkthrough 5.4 Customized Datum Reference Frames and Rotational Constraint 5.5 Free State, Restrained Condition, and Nonrigid Parts
6 Form Controls
6.1 Flatness and Straightness 6.2 Circularity and Cylindricity 6.3 Rule #1, Form, and Size
7 Orientation Controls
7.1 Parallelism, Perpendicularity, and Angularity 7.2 Orientation Zones and Material Modifiers 7.3 Avoiding Unnecessary Orientation and Over-Control
8 Location I: Position and Boundaries
8.1 Position Tolerancing and True Position 8.2 Virtual and Resultant Condition 8.3 Bonus Tolerance at MMC and LMC
9 Location II: Application and Modifiers
9.1 Selecting MMC, LMC, and RFS by Function 9.2 Fixed and Floating Fastener Formulas 9.3 Projected Tolerance Zones 9.4 Coordinate Conversion and Appendix B Position Calculations
10 Location III: Patterns and Allocation
10.1 Composite Position Tolerancing 10.2 Patterns, Simultaneous Requirements, and Multiple Segments 10.3 Slots, Tabs, and Tolerance Allocation 10.4 Coaxial Feature Controls, Concentricity, and Symmetry
11 Profile I: Fundamentals and Strategy
11.1 Profile of Line and Surface 11.2 Defining the True Profile 11.3 Datum-Referenced Profile Strategy 11.4 Equal and Unequal Disposition
12 Profile II: Scope and Verification
12.1 All-Around, All-Over, and Limited Scope 12.2 Composite Profile and Coplanarity 12.3 Castings, Weldments, Sheet Metal, and CMM Evaluation 12.4 Combined Controls and Profile as a Refinement
13 Runout Controls
13.1 Circular and Total Runout 13.2 Datum-Axis Simulation and Rotating Parts 13.3 Runout vs Position, Profile, and Form
14 Exam Strategy and Calculations
14.1 Virtual/Resultant Condition and Bonus Formulas 14.2 Datum Shift and Worst-Case Boundary Calculations 14.3 Functional Gaging and Verification 14.4 Test-Day Tactics, Common Traps, and Review
8.3 Bonus Tolerance at MMC and LMC
Key Takeaways Explain This Topic AI
Bonus tolerance is the extra position tolerance gained as a feature departs from the stated material condition (MMC or LMC) toward the opposite extreme; bonus = |actual size − MMC| for an MMC callout, or |actual size − LMC| for an LMC callout.
Bonus only applies when the position FCF carries an MMC or LMC modifier — never at RFS, where the zone is fixed regardless of size.
For a cylindrical zone, bonus increases the zone diameter directly: effective zone = stated tolerance + bonus.
Bonus is additional geometric (position) tolerance, not additional size tolerance — the feature's actual size must still be within its size limits.
Combining bonus on the considered feature with datum shift on the datum features (covered in Chapters 4 and 14) can dramatically expand the effective location envelope; both must be applied in calculation.
Last updated: August 2026
8.3 Bonus Tolerance at MMC and LMC
When a position (or other geometric) tolerance is modified by MMC Ⓜ or LMC Ⓛ , the stated tolerance is the minimum zone the feature gets — the zone available at the stated material condition. As the produced feature departs from that material condition toward the opposite extreme, the position tolerance zone grows . The amount of growth is called bonus tolerance .
The Bonus Tolerance Formula
For a feature controlled at MMC:
bonus = |actual size − MMC|
For a feature controlled at LMC:
bonus = |actual size − LMC|
Bonus is always non-negative , and it is zero at the stated material condition and maximum at the opposite extreme . For an MMC-controlled feature, the maximum bonus equals the full size tolerance range (MMC − LMC).
How Bonus Expands the Zone
For a cylindrical position zone (hole or pin axis), bonus is added directly to the zone diameter:
effective zone diameter = stated tolerance + bonus
For a two-parallel-plane zone (slot/tab center plane), bonus is added to the width between the planes. In both cases, the zone is centered on the same true position; bonus enlarges the zone, it does not shift it.
Worked Example: Hole at MMC
A hole has unilateral size limits Ø10.0/Ø10.4 (so MMC = Ø10.0, LMC = Ø10.4) with position ⌀0.1 at MMC to A | B | C. The hole is produced at Ø10.3 .
- Produced hole size Bonus = size − MMC Effective zone diameter
- 10.0 (MMC) 0 Ø0.1
- 10.1 0.1 Ø0.2
- 10.2 0.2 Ø0.3
- 10.3 0.3 Ø0.4
- 10.4 (LMC) 0.4 Ø0.5
At the produced size of Ø10.3, bonus = |10.3 − 10.0| = 0.3 , and the effective position zone = stated tolerance + bonus = 0.1 + 0.3 = Ø0.4 . The pattern is general: bonus = |actual size − MMC|, and the effective zone diameter = stated tolerance + bonus. The same arithmetic holds for bilateral limits; only the MMC/LMC values change.
Bonus Is Geometric, Not Size
A common trap: thinking bonus tolerance lets the feature grow outside its size limits. It does not. Bonus is additional position (geometric) tolerance, not additional size tolerance. The actual size must still be within the stated size limits; bonus only becomes available as the actual size moves within those limits toward the opposite extreme.
If a hole is specified Ø10.0 ± 0.2 (limits 9.8/10.2) at MMC, a hole produced at 10.4 has no bonus because it is out of size spec — the feature is nonconforming regardless of position. Bonus is not a back door to expand size limits.
Bonus at RFS: Zero, Always
At RFS (regardless of feature size), the position tolerance zone is fixed at the stated value no matter what size the feature is produced at. There is no bonus at RFS. The 2009 standard uses the Ⓢ symbol (or no symbol as default) for RFS; the 2018 standard uses RMB language. On the exam, if you see no MMC or LMC modifier on the considered feature, bonus is zero.
Combining Bonus with Datum Shift (Preview)
When the datum features themselves are referenced at MMC or LMC, the datum reference frame can shift as the datum features depart from their material conditions — this is datum shift , covered in depth in Chapters 4 (Datum Referencing) and 14 (Complex Datum Applications). Datum shift expands the effective location envelope in addition to bonus on the considered feature.
The two effects are independent and both must be included in a worst-case calculation:
Total location variation = position (with bonus) + datum shift
Datum shift is not bonus tolerance on the considered feature — it is freedom for the entire DRF to translate/rotate. Senior exam items frequently combine the two to test whether you can keep them separate.
Worked Example with Both Effects (Preview)
Hole ⌀10.0 ± 0.2, position ⌀0.1 at MMC to A | B | C, where datum B is a hole ⌀8.0 ± 0.1 referenced at MMC.
Considered feature bonus: actual hole at 10.2 → bonus = 0.4 → effective position zone = Ø0.5.
Datum B shift: datum B produced at 7.9 (its LMC) → datum shift = 0.1 → the DRF itself can translate by Ø0.1.
Total effective location variation = 0.5 (bonus on considered) + 0.1 (datum shift) = Ø0.6 .
The two are additive but distinct; do not lump them into a single "bonus" number.
Senior-Level Traps
Trap 1: Computing bonus from LMC when the callout is at MMC (or vice versa). Bonus is measured from the stated material condition, not the opposite.
Trap 2: Treating bonus as extra size tolerance. It is extra position tolerance, available only while the feature remains in size spec.
Trap 3: Forgetting that bonus is zero at RFS. No modifier on the considered feature ⇒ no bonus.
Trap 4: Adding bonus to the wrong side of the zone. Bonus enlarges the zone (diameter or width); it does not shift the zone's center.
Trap 5: Confusing bonus with datum shift. Bonus is on the considered feature; datum shift is freedom of the DRF. They are computed and reported separately.