He set the rod back on the lathe. “We take it to 29.99. That’s the heart of tolerance, Meena. Not the edge. The heart.”
Limits how "off-center" features can be, usually capped at 0.6mm.
His apprentice, a bright-eyed girl named Meena, handed him the micrometer. “Sir, it’s 29.96 mm. The drawing says 30.0. That’s 0.04 under. Still within the ±0.2, no?” tolerance iso 2768-mk
Tonight, Arjun was making a coupling sleeve for a pediatric ventilator. The client had said “medical grade, but low budget.” Arjun had smiled and pointed to the blueprint. “ISO 2768-mk is the lowest I go. Not a micron more.”
💡 For a part that is 50mm long, an "m" rating allows for a deviation of 0.3mm in either direction. Geometrical Tolerances (The "k" Class) He set the rod back on the lathe
The standard defines four classes of tolerances:
For press-fits or bearing housings, always specify a unique tolerance (like H7/g6) rather than relying on general standards. If you'd like, I can: Compare "mk" vs "fh" precision levels Provide a downloadable PDF summary of the tables Explain how to apply this in SolidWorks or AutoCAD Not the edge
The "m" class ensures that lengths and diameters stay within a reasonable range without requiring expensive, high-precision machining. The tolerance gets wider as the size of the part increases. Nominal Size Range (mm) Tolerance (+/- mm) 120 to 400 400 to 1000 1000 to 2000