Unit 15 Geometric Dimensioning and Tolerancing 265 Copyright Goodheart-Willcox Co., Inc. Material boundary modifiers are applied in tol- erance specifications in a similar way, but they are applied to datum feature references. A material boundary modifier indicates the applicable mate- rial boundary for a datum feature reference. There are three material boundary condition designations: maximum material boundary (MMB), least material boundary (LMB), and regardless of material boundary (RMB). The MMB symbol is an encircled M and the LMB symbol is an encircled L. There is no modifier symbol for RMB. Figure 15‑12 shows the material condition and mate- rial boundary modifier symbols, as well as other sym- bols used in the GD&T system. A material condition modifier symbol appears in the feature control frame following the tolerance, as shown in Figure 15‑13. A material boundary modifier follows the datum feature reference in the feature control frame. When the MMC or LMC modifier is used to modify a tolerance, the application indicates that additional tolerance is permitted for the controlled feature as the feature varies from the MMC or LMC size. The additional tolerance that is permitted as a result of different manu- factured sizes is sometimes called “bonus tolerance.” Maximum Material Condition Maximum material condition (MMC) is the condition of a feature that is at the size limit resulting in the maxi- mum amount of material on the part. MMC means that an external feature, such as a shaft, is at the high size limit (maximum size) and that an internal feature, such as a hole or slot, is at the low size limit (minimum size). Goodheart-Willcox Publisher Figure 15-9. Datum target points on a surface. Datum identifying letter Target number Area size Goodheart-Willcox Publisher Figure 15-10. Datum target symbol. Goodheart-Willcox Publisher Figure 15-11. Identifying datum target areas.