Hitachi's C7BMR 7-1/4 inch pro-grade circular saw features a patented technology called IDI (Internal Double Insulation) to add durability and protect the tool from the harmful effects of vibration. Nothing shortens the lifespan of a tool faster than vibration. IDI is a technology whereby the aluminum housing of the tool is intertwined with an injection molded inner nylon core. This process combines the durability of an all metal body tool with the double insulation advantages of a tool with a plastic housing. Vibration is less wearing on the tool so it lasts longer and safety is significantly improved for the user.