The Roper Whitney CH2420 cheek bender has a two-way trunnion design that holds the bending apron steady at the base of the bend ensuring accuracy throughout the length of the sheet. To change the flange height, the shims are set at the factory to run a flange of 3/16 inch. This dimension can be changed in the following manner: remove the 4 hex bolts on the top plate and change to desired dimension. The adjustable shim will give a range or 3/16 to 5/16 of an inch. This procedure may be done on left and right top plates if desired.