Singer 14HD854 Heavy Duty Serger 2-3-4 Threads, 6 Stitch, Roll Hem, Differential Feed, Metal Frame, 60% Larger Cutting Knife, 1300SPM

Movable Upper Knife Upper knife can be engaged to trim excess seam allowance as you sew, or it can be rolled out of the way for special techniques like flatlocking or anytime when you don't want the machine to trim