Barely, maybe never, used. 

Interesting article about various brand interoperability.  The Kingpin will essentially fit all "dynafit" style attachments (6mm bar with a single centering notch. Some variations on the 6mm with a single notch are how much room is located behind the bar (the more room, the more interoperability // the less room, the less interoperability); the Kingpin has more than some, less than the standard "dynafit" bar. 

90mm and 105mm

$70 $60 each pair shipped or $130 $115 shipped for both pairs

Cheers,

Dave

( 2-THREE-9 ) 2-THREE-3 - 2-ZERO-ZERO-2