Approx. 3.75"

STS-51-L was the 25th flight of the American Space Shuttle program, and disastrous final mission of the Space Shuttle Challenger, which lifted-off from Launch Complex 39-B, at the Kennedy Space Center in Florida, on January 28, 1986. The mission ended in catastrophic failure with the destruction of Challenger, starting at 73 seconds after lift-off, and the death of all seven crew members. The Rogers Commission determined that the cause of the destruction was due to the failure of an O-ring seal on the starboard Solid Rocket Booster (SRB).