If you want to make one, here’s how:
1. Make a slip stitch, chain 4, join in a circle.
2. Make 12 double crochet (or single crochet to you US folks) into the ring
3. (Chain 2, 4 DC) and repeat twice more. Now you have your triangle shape.
4. Just keep going around in DC and at the corners, (DC, 2 chain, DC). Keep going till you have the size of the seat top.
5. Now DC without corners for 4 rounds.
6. Now treble all around for 2 rounds, finish off.
7. Thread elastic through the last round and knot tightly when the cover is pulled firmly over the seat.
It matters not your yarn or your hook size, just use whatever scraps are to hand…it is a bike seat cover.