I've got a 300m and having the same problem. I've bought two sets one from scosche and 1 from metra. Scosche didn't line up right and the metra my speaker didn't fit in the hole so I cant mount them right. Looked into modifying the plastic but it would need to be destroyed. Just drilled them right into the plastic until I can get some mdf and free time to make some myself.1/4 might be to big. if my speaker stuck out any more the factory grill won't stay on.