A 2x4 LEGO brick from 1958 still snaps perfectly with today's bricks, thanks to maintaining mold tolerances of 0.01mm across billions of parts annually. This precision - where a brick just 0.02mm off-size fails functionally - represents an extreme case study in manufacturing consistency that most consumer products never face. For hardware engineers, LEGO's system demonstrates what's achievable when dimensional consistency is non-negotiable.

LEGO achieves this through hardened steel molds cut with wire EDM, achieving tolerances within microns. Each cavity is numbered and tracked, allowing defects to be traced to their exact origin. The company uses scientific molding with rigorous process control - monitoring every phase from filling to cooling - rather than relying solely on precision machining. This focus on stability over absolute precision allows LEGO to maintain consistency across multiple global factories. Different pigments affect shrinkage differently, with dark colors shrinking 5-10% more than light colors, creating challenges like the 'brittle brown' problem.

LEGO's commitment to interchangeability creates both engineering constraints and manufacturing costs. The 8mm grid system, 4.8mm studs, and brick heights in multiples of 3.2mm limit geometric freedom but ensure universal compatibility. This philosophy generates 2-5% scrap rates - billions of rejected parts annually - but preserves the brand promise. The key insight is that process control beats precision machining: a stable, repeatable process produces better results than chasing the tightest possible mold tolerances.