I designed this motor bracket with Jerry Hill http://www.steadimoves.com to solve the problem of having the motor slip on the iris rods. When I use the motor on 15mm rods with the 19mm - 15mm insert, the motor tends to slip off of the gear, especially while calibrating. This Hill bracket is "Rock Solid!" We wanted to keep it simple and without any modification. The rosette spool fits into the original Cmotion 19mm clamp and absolutely will not slip but allows another point of adjustment. The motor can be rotated and moved up and down the dovetail. The rosette gives you numerous additional adjustments. The Hill Motor Bracket is so strong that you can even pick up the camera using the motor bracket and not have the motors slip off of the lens gear! The bracket arm can be easily mounted on either side of the motor rosette spool. Jerry can supply kit with either 15mm or 19mm or Panavision 5/8" arms.