For floaters 6wt and above and all my sinking lines i use Moser minicons, brilliant little beasties
And at about an inch long they dont affect the characteristics of the line.
On lighter lines they do affect the balance so use a needle knot like Hamish, although
instead of a needle or nail try using a short section of tube, ie the centre of a cotton bud or the like
it makes life much easier
Sandy