when converting an original, working, sending unit to a 3/8 or 1/2" tube, unsolder the sending unit first. mark the relationship of the original tube so the replacement will be in the original orientation. then, unsolder the tube from the retaining flange. bend the replacement tube of the size of your choice to match the original tube. next, using a tapered punch ONLY, open up the original hole in the retainer to obtain a slight, "drag" fit on your replacement tube. the reason for using a tapered punch instead of a drill bit is two fold. #1, a drill has the real possibility of catching and spinning the retaining plate, thus messing up the hole as well as the plate. second, and most important, the taper punch will add extra strength and support to the replacement tube due to the extra solder being used to solder the tube to the plate. just support the underside of the plate so as to not bend it, and use silver solder only for attaching the tube and sender unit. hope this helps. i have done many of these upgrades over the years, even on other makes.