displaced relative to the cogs of the associated primary ratchet wheel 30 as illustrated in fig1 a and other figures the bridging members in the preferred embodiment will be auxiliary ratchet wheels 40 similar in construction to the primary ratchet wheels 30 with corresponding centroidal opening 44 a radial slot 44 b and cogs 42 each auxiliary ratchet wheel 40 is rotatably mounted to its corresponding primary ratchet wheel 30 so as to be rotatably operable between the open and engaged positions in the preferred embodiment as particularly illustrated in fig2 and 4 this rotatable operability is facilitated by providing a pair of arcuate slots 46 in each auxiliary ratchet wheel 40 and providing a stop post projecting through each arcuate slot 46 and anchored to the corresponding primary ratchet wheel 30 as illustrated in fig1 a the stop post may be a machine bolt 54 with or without washer 56 which engages a mating threaded opening 36 in the corresponding primary ratchet wheel 30 however it will be readily apparent that the stop post could take any of several other forms the arcuate slots 46 and stop posts are configured such that when an auxiliary ratchet wheel 40 is rotated in one direction until the stop posts hit the ends of their arcuate slots 46 the auxiliary ratchet wheel 40 will be in the open position and when the auxiliary ratchet wheel 40.