as illustrated on an enlarged scale in fig4 6 each selector finger 30 is replaceably supported by a generally u shaped carrier 32 secured to one associated sleeve 28 it will therefore be seen that the selector fingers 30 can pivot up and down with the bidirectional rotation of the associated sleeves 28 on the fixed shafts 26 employed for the desired bidirectional rotation of the sleeves 28 are a plurality of eight in this embodiment pairs of electromagnet assemblies 34 and 34 39 immovably supported within the support frame 22 each electromagnet assembly 34 or 34 39 comprises a magnetic core 36 or 36 39 with a coil 38 or 38 39 wound thereon fig6 best illustrates that each pair of electromagnet assemblies 34 and 34 39 extend horizontally with one 34 positioned over the other 34 39 and with their ends held opposite one of the rotatable sleeves 28 as will be understood by referring again to fig3 the eight pairs of electromagnet assemblies 34 and 34 39 are arranged in two diagonal rows it will further be noted that every two pairs of such electromagnet assemblies are in vertical alignment with the four electromagnet assemblies of each vertical series disposed at substantially the same pitch furthermore the successive vertical series of electromagnet assemblies are vertically displaced at half the pitch from the neighboring series so arranged the eight pairs of electromagnet assemblies 34 and 34 39 lie opposite the eight rotatable sleeves 28 respectively which are disposed with minimal spacings therebetween such an arrangement of the electromagnet assemblies 34 and 34 39 makes.