Dear Heath,
The 5/16 ferrules with flanges (Fender Vintage Ferrules fit perfectly) are easier to manage because they seat at the same depth in the flange seat. The 3/8 ferrules can be a bit harder to seat all at the same depth if the bores are deep or irregular depth. If you are going to spray the body remember to mask the holes (Bluetac works for me) well and take the sharp edge of the bores to allow a little lacquer build around the edge of where the ferrules will go in. Regards, Russell.