Full definition
The permissible range of variation in a manufactured part dimension, defining the acceptable limits within which the actual measured size must fall. Tolerance = Upper limit - Lower limit. Expressed as bilateral (±) or unilateral (+0/-0.1 or +0.1/-0). Tighter tolerances require more precise manufacturing processes and more rigorous inspection, directly increasing cost. ISO tolerance system: IT01 to IT18 (IT = International Tolerance grade), where IT01 is the tightest (sub-micron, gauge blocks) and IT18 is the loosest (rough castings). Typical manufacturing capabilities: CNC machining IT6-IT8 (±0.01-0.05 mm), grinding IT4-IT6 (±0.002-0.01 mm), rubber molding IT10-IT14 (±0.1-0.5 mm), die-casting IT8-IT12. For rubber products: RMA (ARPM) publishes standard tolerances by product type — molded rubber typically Class A1-A4 (closest to loosest), extruded profiles ±0.2-0.5 mm on cross-section, die-cut gaskets ±0.5-1.0 mm. For V-belt pulleys: groove dimensions per ISO 4183 with tolerances, bore tolerance H7 (standard fit) or H8 (loose fit). Over-specifying tolerances wastes money; under-specifying causes fit and function problems. Per ISO 286 (limit and fit system), ASME Y14.5 (GD&T), and RMA tolerance standards for rubber products.