PFC is a C-section steel beam with two parallel flanges and a web between them. Sized by the web depth: PFC 75, 100, 125, 150, 180, 200, 230, 250, 300 mm. The corresponding flange widths and thicknesses scale up roughly with the web depth.
PFC turns up in balustrades as a heavy base post or perimeter beam, in gate hardware as a track ledger for very large sliding gates, and in commercial work as a column splice or stair stringer. The taper-flange version (TFC) is older legacy stock from the imperial era, mostly replaced by PFC in modern Australian steel.
PFC is overkill for most residential gate frames but the right call wherever the bending moment in one direction is high and you want a flat surface to bolt other steelwork to.