To tighten the Hiya Hiya I use one of the jar lid tightener pads. Part on the needle and part on the cable. So far I have not had any problems so far and like the ability to get needle that are 4 inches (10 CM). I knit socks and dislike the longer needles of the other interchangeable.
You may want to stop by Raverly and check into the Hiya Hiya forum. And I know that the people at Hiya Hiya read it. It would be good for them to hear from there customers.