Investigators found that when the windscreen was installed 27 hours before the flight, 84 of the bolts used were 0.026 inches (0.66 mm) too small in diameter (British Standards A211-8C vs A211-8D, which are #8-32 vs #10-32 by the Unified Thread Standard) and the remaining six were A211-7D, which is the correct diameter but 0.1 inches (2.5 mm) too short (0.7 inch vs. 0.8 inch).