Bethlehem steel, n. — Green’s Dictionary of Slang

Bethlehem steel n.

[play on name of the US steel manufacturer]

(US black) a boastful description of the rigidity of one’s erect penis.

1983		R. Klein Jailhouse Jargon and Street Sl. [unpub. ms.].
1997		Solar Project ‘Zeitgest’ 🎵 on ...in Time [album] You wanna feel my Bethlehem steel / Mary Poppins, TNT, Bristol City / I bite into your cats and kitties.