Up for 'buy it now' is a Ridgid Style 3RSB Heavy Duty well made Rotary Saw Blade Set. Designed for cutting roots and plowing through heavy debris. Fits K-375 K-380 K-400 K-50 K-3800 and other 3/8" and 1/2" cables running a 5/8" cable end, not cable size.   You won't find a better root bit period!