[EN 12792-2003, 120]:components of ductwork incorporating one or several of the following changes relative to:- the length of the duct;- the orientation of the duct;- the shape of the straight length of the duct;- the area of the cross-section of theduct.Examples of duct fittings are:- Bend or elbow;- Transformation;- Branch.NOTE Apart from rigid components of ducting there are flexible sleeves which reduce the propagation of mechanical and/or acoustic vibrations between two components or ease the assembly of the installation.