This jaw can be added to Mega Complete Retrofit System BC stands for 'bottom control' and is comprised of a carbide insert that acts as a deflector to keep blades from varying to far out of the cut when miscuts takes place. Distance between the bottom of the blade and top of the bc jaw is set using 4 setscrews. This jaw rides just under the blade and the only time they touch is when the blade deviates out of the direct line of cut. This system quickly pays for itself by keeping a blade from diving straight down into the log. You will need one for each guide making a total of two.