33 and whose remaining end is designed to act on said engaging component 20 via a thrust bearing 45 another possible way of embodying the mate at 34 not illustrated would be through matching conical surfaces likewise breasted the forward amp reverse drive thus composed functions as follows assuming transmission from input shaft 2 to output shaft 3 in which case there will be a prime mover attached to input shaft 2 and a service to output shaft 3 an ideal example of which would be the screw driven by a marine engine although the drive gear as described may serve equally well for any application of related type including those where drive is transmitted from shaft 3 to shaft 2 with the control collar 23 in its central neutral position illustrated in fig1 both clutch mechanisms 12 amp 13 are disengaged and input shaft 2 will simply turn the two primary gears 6 and 7 in opposite directions whilst secondary gear 9 fixed to output shaft 3 remains isolated from both the latter for secondary gear 9 to engage with primary gear gear 6 control collar 23 needs to shift to the left as viewed in fig1 this being achieved by applying slight pressure thereto sufficient to displace locating elements 25 from their seats 27 by urging them against their single springs 26 whereupon canted surfaces 28 offered by said locating elements 25 will be caused to mate with canted surface 31 offered by collar 23.