i think hyper 9s come with 19 mm, not sure .... O'donnell also makes 17mm shocks that are really good (better than Ofna 17mm IMO) BUT us team guys and alot others are now running the OD 17mm shocks the sleeve in them to make the bore to 16mm, works alot better than 17mm, i think 16mm shocks are better than 17mm or bigger IMO.