Start with what a grille is: a frame of blades at the end of a duct, aimed at a room. Everything else follows from what the blades are allowed to do. A fixed-bar grille has blades locked in position: nothing to adjust, nothing to break, the right choice for return and exhaust air where direction does not matter. It is the workhorse you never think about, and correctly so.
A double deflection grille has two sets of blades, one behind the other, turning the air both horizontally and vertically. This is the supply grille you want when the air must miss a desk, a bed or a doorway: the commissioning engineer aims the pattern once, and it stays aimed. Linear bar grilles stretch that idea into a continuous line for architectural perimeters and under-window runs, where a sill grille in an aluminium frame also guards the heating element beneath it.
Floor grilles live the hardest life of all: heels, chair castors and cleaning trolleys. They are extruded heavier, mounted flush, and still expected to direct air. Our guidance never changes: tell us the room, the mounting height and who walks on it, and the grille type picks itself. What we then fabricate is sized to your opening, not to a catalogue page.