t-bulb

from The Century Dictionary.

• noun A name given to bars or beams of iron or steel having a cross-section like that of a T-bar, except that the vertical flange corresponding to the stem of the T is thickened by an ovoid or elliptical reinforcement, making its cross-section resemble a vertical section of a bulb with an upwardly extending stem attached and filleted to the horizontal flanges of the bar or beam. Such bars or beams are used in ship-building and for other purposes.