Ideal for odd sizes.  What I didn't realize is that this adapter is made from a rubber like compound, not the hard plastic used for almost all adapters.  It is conformable and you simply cut off (I used a hack saw) the portion you don't need.  I had an odd coupling between a Festool vacuum and a small Jet sander and this is the only way I could make the connection work.  The cut end is rough and I suppose I could use a sander or fine knife to trim the edge but it hasn't proven necessary.  Quality is good, material is conformable, highly recommended.