Wow, sorry this went unanswered. I just dont know myself so thanks Cad for the 411. I might add that the IBTipsys are a very snug fit so that would even make them tighter but they are certainly not required. One thing to keep in mind though is you can always change orings to change fit on anything that is sealed with them. The IBTipsy for example uses a 1.5 x 5.5 so a 1.5 x 5 with stretch and fit a little looser.