preferably between 5 and 5 u00bd inches and spaced in an interval of every 2 inches the recesses 7 are set about 1 inch from the rails in order to match with the pair of holes 9 in the slideable member the slideable member 4 depicted in fig3 is 24 inches in width 5 u215e inches across and 11 16 inches thick the slideable member 4 has notches 3 such that the space defined by the tongs thereof are of similar width to those of the base member 1 the thickness of the notches 3 shown in fig3 may be less than the full thickness of the slideable member 4 or the notches 3 may be fully as thick as the slideable member 4 itself in this example a groove matching the dimensions of the spline 6 which in this example is u215b inch thick is provided on the lower surface of the slideable member 4 as depicted in fig5 the slideable member 4 has two pairs of recesses towards one end for adjustably affixing the extension member 5 only one pair of recesses being utilized at a particular time depending on the desired door buck spread width the slideable member may have three pairs of recesses 2 inches apart to allow for adjusting the extension.