Have you got a Micro-Mark product number so we know what you're asking about? I think they sell more than one x-acto knife blade "with teeth" as a saw blade.
I have a couple of toothed blades, and they do not fit the standard x-acto knife handle because their shank is wider than a #11 blade. I have an old alumimum handle that takes these larger blades.
The blades shown on page 84 of Micro-Mark's Holiday 2007 catalog clearly indicate which handle they require, so you need to know which blade you have and then get the appropriate handle. X-acto and others obviously make many different sizes of handles.