The STF-1 spacecraft is so small that on multiple occasions, measurement errors of less than a quarter millimeter have caused concern. One example of this occurred during the model review of the battery unit. The EPS was colliding with the chassis as highlighted in the image below in blue. The fix for this was as simple as ensuring the connectors were fully mated, but even adjusting the EPS this much caused the entire spacecraft to have to be rechecked. 
To provide some scope, on average a grain of sand is 0.5 millimeters and the head of a pin is 2.0 millimeters. The STF-1 spacecraft has some very small components with low tolerances. Even forgetting to include washers will cause issues during assembly. Currently the STF-1 team is focusing very hard to ensure we use every piece allocated as the spacecraft gets constructed unit by unit from the top down.