Tolerance Zone Material Requirements (ISO)

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For a datum reference frame in which a referenced datum feature is a feature of size, you must specify a material requirement (MMR, LMR, RFS, or RPR) for the tolerance zone. Keep in mind that for MMR and LMR, the collective requirement concept applies, allowing for additional tolerance.

The function of the workpiece is the primary factor for material requirement selection. The table below provides a guide for deciding where MMR, LMR, RPR, or RFS should be indicated. One of the most common functions for the workpiece is assembly (e.g., the feature of size is assembled to another feature of size); therefore, MMR is the most common tolerance zone material requirement.

Requirement	Common Functions	Collective Requirement Applies	Relative Cost to Produce or Verify
Ⓜ	• Assembly • Location of non-critical feature of size	Yes	Low
Ⓛ	• Wall thickness • Minimum distance • Minimum machine stock	Yes	Medium
Ⓡ	• Location of non-critical feature of size	Yes	Low
<RFS>	• Centering • Alignment	No	High

Note that RPR, Ⓡ, may only be used in conjunction with MMR, Ⓜ, or LMR, Ⓛ.