Space Shuttle Endeavour STS-118 Impact Damage

Source: NASA Orbital Debris Program Office

Older news from the Orbital Debris Quarterly News, Volume 12, Issue 1, January 2008:

Early impact test results suggest that the particle size was approximately 1.5mm to 2.0mm in diameter, assuming that the particle was orbital debris.

An impactor, maybe 1.5-2.0mm wide, creating a whole ~1⁄3 in wide through thin layers of an aluminum honeycomb radiator and silver teflon tape.