the other way is to plait them. Start the same by knotting one end and putting over a conveniant hook. Then plait away.
In my youth I used to get fancy and do a plait with 4 strands ! But 3 is simpler
You can make a simple loop at one end before you start to plait - knot the ends. Then leave a space and knot again a little further down. You end up with a part that has strands rather than plait. Then you can just feed the loop through a ring, feed the plait through the loop - and the whole thing is now attached to the ring.