a strut or part shaped like a T
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Examples from the Web for t-piece
On the top of this is a cross or T-piece, which serves to extend the top of the tent, 6ft.
The vertical limb of the T-piece is narrowed down at its lower extremity and opens by a small aperture.