t-head

from The Century Dictionary.

• noun A cross-bar fastened at its middle to a chain, as a watch-chain, tracechain, etc., for use as a fastening by passing it endwise through a hole, ring, or link and then turning it into a position which prevents its withdrawal.
• noun A short bar welded or riveted to the end of another bar at a right angle, as in a form of anchor for masonry.