of the base member 10 as best shown in fig4 the slide member defines a hook or sleeve 50 52 extending from each side edge 46 48 respectively and bent downwardly and inwardly to form a sleeve adapted to engage the corresponding side edges 22 24 of the base member 10 a stiffening rib 54 is shown in fig3 formed in the sleeve member extending longitudinally between the first end edge 42 and the second end edge 44 to impart rigidity to the sleeve member the operation of the adjustable shim of the present invention is best illustrated in fig5 through 8 this device is usable in the construction industry where carpenters require shims for spacing or otherwise orienting window frame units or door frame units in the rough openings formed of lumber in a wall other uses for the adjustable shim will become apparent to the user for purposes of example we will designate as 56 the fixed member representing the frame formed in a wall and as 58 the movable member representing the side of the window frame unit after the wall 56 is in place and it is desired to install a window or door frame unit in place with an appropriate spacing between the fixed and movable members the base member 10 is affixed to the fixed member 56 as for example by nails screws or other commonly used fasteners the fastener is positioned through the aperture 38 and extends into the fixed member 56 this secures the lower surface 16 of the base member flush with the outer surface of the fixed member in this orientation the entire base member.