What is the black box on the handles in the pictures?
This is a Speed Control and this option eliminates the need for a foot pedal to operate your sewing machine. It is available for the Juki: TL98E, TL98Q, BabyLock QP, Brother: 1300, 1500, Janome: 6500, Pfaff: 1067, 1069, 1171, 1371, 1467, 1469, 1471, 1472, 1473, 1475, 6230, 6250, 7510, 7530, 7550, 7562, 7570.