Some technical notes on Lego:
Lego is designed on an 8mm grid. Which is to say that from the middle of one bump to the middle of the next is 8mm (16mm for Duplo). However, it is slightly less by ~0.2% (16 microns in 8mm) - perhaps something slipped when they changed from Cellulose Acetate to ABS. If they had just ignored the mould-shrinkage difference and continued to use the same tooling then they would have been almost exactly 16 microns over.
However, it is not clear what could have slipped - it is as though they had designed for the standard ABS shrinkage of 0.5% but instead chose a formulation that shrank 0.7%, not likely but possible. But in any event we have an anomaly that can drive competitors / collaborators to distraction (trust us on this one). This is a true anomaly in that Lego tooling is designed (supposedly) to a 5 micron (.0002") tolerance.
Some dimensional data:
- A 2x4 Lego brick measures ~16mm by ~32mm by 9.6mm high.
- The distance from stud center to stud center is ~8mm (but see above).
- The diameter of a LEGO stud is ~5mm
- The height of a stud is 1.7mm.
- The walls of LEGO bricks are 1.5mm thick, while the walls of the tubes are ~657 microns thick.
- LEGO has reported that they build their molds to a 5 microns tolerance (this is usually tightly-guarded proprietary information - and while it is clear that Lego parts are molded to tight tolerances - but see above, they are off by 16 microns every 8mm nominal).