I contacted Lippert for measurement comparison. The Trailair Flex Air 5th Wheel Pin Box, # LC369535, has a distance from bottom of king pin to top of box measuring 19.56" (king pin length approx. 4"). The Trailair Rota-Flex 5th Wheel Pin Box, Lippert 1621, # LC328329 drawing shows measurement of 13.54" from top of kingpin to top of box (king pin length approx. 4") 13.54 plus 4" being 17.54" will provide you an approximate drop of only 2". I don't think this gets you where you want to... view full answer...
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