I have a 3o/10 size return.I need grill for it?

Unless you have a little two-ton air conditioner you need to re-size that return to a standard size of 30x30 or something else twice the area of the inside unit's footprint (the size of the bottom of unit when upright where return air enters). This will make the unit cool better and you can use pleated filters. I would get a filter grill for 2 inch filters.