A bend former is sometimes referred to as a bend die. This is the main tool around which the tube is bent. It has the shape of the tube machined around the periphery to contain it during the bending process. The radius from the centre of the former to the centre of the tube is referred to as the CLR (centre line radius). Bend radius may also be referred to by the relationship of the tube diameter to the CLR. For example 60mm diameter tube bent on a 180mm CLR would be referred to as a 3D bend (3 x tube diameter = 180). Similarly the same 60mm tube on a 60mm CLR would be a 1D bend.
The straight section of the bend former is called the former extension. This may be machined as one piece or be detachable. If detachable it can be replaced with a different type of gripping surface. The bend radius and the resistance of the tube to be bent determine the extension type selection. As a generalisation the tighter a bend radius is the longer the clamp area needs to be to overcome the additional resistance, although serrations or coating the gripping face will assist in keeping the length to a minimum.