For Standard seat posts, the ones that fit a saddle clip onto the top of the post (7/8"/22.2mm at that part) rather than the toothed steel ones
there are thanks to Brompton for their folding bikes designed a single bolt light alloy saddle clip ..

Rather than a single friction fitting , they use a multi-plate affair like the dry clutch on motorcycles
all those plates hold tightly

Setback, 2 bolt integrated seat posts , Campagnolo .. hard to top Tulio's design ..particularly with leather saddles ,

the bolt head on top is hard to reach with plastic saddles ,

but Leather ones folding up the sides to stick a wrench on there is simple..