Abstract: A tube bending apparatus of the radius block and slide block type is provided with a one-way drive means for permitting selectable driven rotation of the radius block means thereof in the bending direction while preventing reverse driving. Interchangeable radius block and slide block means are provided to accommodate different size bend radii and tube diameter to be accommodated. The apparatus also includes slide block retainer means for accommodating different height slide blocks, as well as tube clamping means for accommodating different tube diameters. The slide block means may be marked with indicia for aiding in the gauging of center-to-center dimensional gain in finished 45 and 90 degree forward and reverse bends prior to forming the bends. A method for pre-gauging center-to-center dimensional gain of such bends is also described. A second embodiment of the tube bending apparatus includes radius block and slide block means having inclined concavities for forming radiused overlapping 360 degree bends.