with other connector elements e g quick lock fittings a shaft and a sleeve secured together by a set screw or a squared shaft and groove it should also be noted that in alternative embodiments linearly movable frame 320 may be configured such that the rotational axis of tray holder 321 is disposed perpendicular to guide rails 508 and 511 in this embodiment stationary arms 337 and 338 may be replaced by a frame including rear and front support beams e g a box frame wherein rotate adapter 352 and pivot pin 360 are mounted on rear and front support beams respectively referring to fig1 a vertical home photo sensor 370 for example a u type photoelectric sensor is preferably mounted on side gussets 323 facing back bar 336 a vertical home flag 371 mounted on back bar 336 cooperates with the home photo sensor 370 to indicate when the back bar 336 is at its high or vertical home position a similar photo sensor referred to as a rotate home photo sensor 372 is preferably mounted on a lower left portion of the back bar 336 the rotate home photo sensor 372 cooperates with a vertical home flag 373 mounted on a designated corner of the tray holder 321 to determine a home rotate position for tray holder 321 accordingly rotate home photo sensor 372 indicates whether a.