K'nex Jump Arm Lift.

[@StickTrickDominoDude]

So amazingly cool!

[@Thibault_Art]

Thanks.

[@geeknightscom]

Where did you get the black and red ball?

[@Thibault_Art]

Geoffrey Barth I found the black K'nex balls on a second-hand website. The red balls are from the K'nex Big Ball Factory building set.