a multiple of the diameter of the driven sprocket 60 in the embodiment disclosed in fig1 the sprocket 62 has twice the diameter or twice the number of teeth of the driven sprocket 60 so that the hooks 50 are reciprocated twice as many times as the needle 20 is reciprocated the angular positions of the respective eccentric cams 38 and 58 on their corresponding needle shaft 39 and hook drive shaft 59 are so oriented that the needle and hook drive mechanisms are synchronized so that the needle 20 is in a lower position penetrating the base fabric 15 while the looper 50 is in a forward position crossing the needle 20 as illustrated in fig1 and 3 for engaging the yarn loop 44 in one form of the looper 50 a bill 64 having an upper edge 65 and a lower edge 66 generally converging forward to a point 67 projects from a throat portion 68 the throat portion 68 forms an integral extension of the shank 51 the top edge portion of the looper 50 may be laterally curved or indented to form a dished out portion 69 to facilitate guiding the needle 20 on its downstroke past the looper 50 also preferably formed in the intersection of the lower edge 66 and the front edge 70 of the throat portion 68 of the looper 50 is.