car is my mates and he asked for new caps when he bought the car, they are completely loose and floating around. Unlike ours these press fit into the centre of the hub whereas ours press fit at the outer point of the caps.
The ST170 ones do seem to have outer clips (like ours) but they do not appear to go under the rim and just but into the wheel. I can't see anything wrong at all, rattle like hell, all four are the same.
See attached picture.

If i remember right they just need a really hard wack. The metal rim behind the cap is what holds them in place

they do seem to plop in well then become floating, the picture is exactly how they all are hanging out.