Hi Marv, I'm not sure if I understand - do you mean you want to fillet only this one piece shown selected here? :



If so it's not really feasible to fillet that edge alone because it would cause the fillet to open up holes in the ends of the fillet, see here for a related example:
http://moi3d.com/forum/index.php?webtag=MOI&msg=5091.4

It is possible to generate a fillet surface to work with though by using surface/surface filleting instead of edge based filleting. To do that use Edit > Separate on your object to break it up into individual surfaces and select 2 surfaces to fillet. That can generate a fillet surface in situations where edge based filleting will not.

But if you do that here the 0.3 radius fillet is still too large to fit totally inside the available area. You could use it as a cutting surface in boolean difference to make something like this though, is this what you're trying to do? (3DM file also attached):



- Michael