What inch trailer do you need for what ounce jig, for example what would you need for a 1/4 or 3/8 ounce one

Anywhere from 3-4 inches is what i use for both of those sizes. You can cut a little off too suite the size of the jig/hook. 

3.50"

I usually use a keitech 3.8 on most of my swimjigs. I also use 4 and 5 inch grubs. I generally am using 3/8 and 1/2 heads though.