Wood saws are categorized by their teeth shape and the number of teeth per inch (TPI). The higher the TPI of a saw the finer the cut it will make. Crosscut saws utilize knife-shaped teeth that cut across the grain of the wood while rip saws cut with the grain using chisel-shaped teeth that rip the wood cells apart as the cut is made. The kerf (slot) made by by a crosscut saw is much smoother than that made by a rip saw but a rip saw cuts much faster. Coping saws are a type of bow saw used to make detailed often curving cuts using replaceable blades with fine small teeth.