[Lynn Eades]

Just trying to help Petr. The next thing is that the seat cushions go around the other way, with the rounded corners to the front. (I used to think they should go in the way you put them)
Those anti slap springs are just a flat leaf that goes up slightly as it goes rearward from the bolts. they hold the rod above the bolt heads. The rear end flattens out.
A guess from my computer chair, I'd say they are about 120mm long x about 21mm wide, and possibly a little thinner than the throttle spring leaves.
I have a picture somewhere but not able to find it yet.
There are covers that go over the rods as well.