of upper base 84 when walls 110 112 are in the article engaging position as shown in fig4 in addition cam wheel assemblies 234 236 are mounted in a cam wheel receiving space 228 formed on the distal portion 98 of each arm 92 94 as shown in fig3 which specifically shows leading cam wheel assembly 234 each cam wheel assembly 234 236 includes a cam wheel 100 that is formed to include two rims 238 that define a channel 240 therebetween as shown best in fig6 an o ring 242 made from a resilient material is received in channel 240 o ring 242 provides traction for cam wheels 100 against wheel guide tracks 42 to ensure that each cam wheel 100 rotates while engaging wheel guide tracks 42 to minimize drag forces on carrier chains 12 and to minimize wear on cam wheel assemblies 234 236 use of o rings 242 is especially advantageous because contact between cam wheels 100 and wheel guide tracks 42 can result in wear of the contacting surfaces interposing soft and easily replaceable o rings 242 between cam wheels 100 and wheel guide tracks 42 results in wear of the easily replaceable o rings 242 rather than wear of wheel guide tracks 42 or cam wheels 100 bearings 248 are press fit into an opening 244 formed in each cam wheel 100 and an axle 246 is received by bearings 248 and is fixed to a mounting block 250 mounting blocks 250 are fixed to arms 92 94 to mount cam wheel assemblies 234 236 to arms 92 94 arms 92 94 include a center line 146 bisecting the ends 142 144 of arms 92 94 as shown in fig2 cam wheels.