of gravity of the rod box 128 fig1 a and 11 b illustrate one of the indexing assemblies 140 in isolation from the horizontal directional drilling machine 120 the depicted indexing assembly 140 includes one of the feed structures 144 and one of the blocking structures 146 as shown in fig1 a and 11 b a hydraulic cylinder 195 is provided for moving the feed structure 144 between the retracted position shown in fig5 a and the extended position shown in fig5 b however it will be appreciated that other types of drives e g rack and pinion drives chain drives etc could also be used for certain applications it is desirable to block one or more of the pockets 131 b 133 b of the feed structure 144 so as to prevent rods from entering the pocket structures 131 b 133 b this function is provided by the blocking structure 146 the blocking structure 146 is mounted between the feed structure 144 and a guide member 197 the guide member 197 is substantially parallel to the feed structure 144 the blocking structure 146 includes a top blocking surface 199 preferably positioned at the top of the feed structure 144 preferably the blocking surface 199 is sufficiently long or otherwise sized shaped to be capable of concurrently blocking all but one of the pockets e g pockets 131 b 133 b the blocking structure 146 also includes a pin 200 adapted to fit within openings 201 204 defined by the feed structure 144 the pin is.