The difference between a Wafer and Lug type body Butterfly valve is only the provision of mounting of valve at pipeline. Lug type valve has lugs that are used to mount the valve to lugs that are attached the flanges on then ends of sections of pipe so that each length of pipe can be removed and replaced independently. Lug Type Butterfly Valve have main advantage is you can disconnect any flange of pipeline.
Lug-style valves have threaded inserts at both sides of the valve body. This allows them to be installed into a system using two sets of bolts and no nuts. The valve is installed between two flanges using a separate set of bolts for each flange. This setup permits either side of the piping system to be disconnected without disturbing the other side.