Titanite
Referenced in ultimately unused dialogue from the final draft script of the  first season episode , titanite was a strong substance used in the creation of plates which formed the hulls of Class F shuttlecraft.

When Lieutenant Boma expressed fear that the plates of the shuttlecraft  would be smashed in by a Taurus II anthropoid, Spock stated that the plates were titanite and added they would therefore hold, at least for a while.
Unused production material