female member 22 when the male member 25 is engaged with the female member 22 fig1 shows an external side 27 of the male member 25 that will face the outside of the rough in box 28 shown in fig2 and 21 fig2 shows the male member 25 fully inserted into the female member 22 giving a minimum length for at least one side wall of the rough in box 28 the male member 25 is slidably engaged with the female member 22 such that the length of a side wall formed by the male member 25 and female member 22 can be adjusted fig2 shows the partial withdrawal of the male member 25 from within the female member 22 to provide a side wall unit of an adjusted length once the desired length of the side wall of the rough in box 28 is obtained the female and male members 22 25 are secured to each other by a pin dowel or nail a specific type of fastener may also be used that is spring loaded to allow for quick manipulation or a quarter turn fastener may also be used to allow for quick manipulation fig2 shows a square rough in box 28 having all four sides with a minimum length when the male member 25 is fully within the perimeter of the female member 22 fig2 shows the rough in box 28 with the male members 25 partially withdrawn from the female members 22 thereby giving a rough in box 28 of an adjusted length and width both the female and male members 22 25 are provided with a flange at the top 38 39 and each flange.