The shell can be fixed on different frames:
4 legs metal frame, stackable, with integrated armrests;
swivel, with gas lift for height adjustment and base with castors;
with folding writing tablet in ABS or HPL integrated into the 4-legged frame;
with fixed HPL writing tablet;
with magazine rack integrated into the 4-legged frame;
modular bench (possibly equipped with armrests and coffee table)