The Adjust-A-Trim isn't the only adjustable steel door jamb on the market, but it's the only one that comes with a prehung door. Most steel frames have to be assembled on site; if you wanted a prehung steel door, you've always had to be satisfied with a wood frame. But the Adjust-A-Trim changes all that. The system comes in two pre-assembled halves. The base jamb is installed from the inside and is prehung with a 22- or 24-gauge galvanized steel, insulated door. The closure jamb slips in from the outside, its edge fitting into a channel in the base jamb that permits 1/2 inch of depth adjustment. Both jambs are fitted with nonremovable metal casings. The Adjust-A-Trim comes