22mm Low Profile Clamping Monster Horn:
This low profile horn sits as close to the servo case as possible.  Servo cases vary in design, so you must verify the horn does not make contact with case. You must be sure the screw you use to connect the steering link to the horn does not protrude through the horn as it will make contact with the servo case. 
Super strong 4mm thick 7075 Aluminum
Weight: 4g
M2.5 clamping bolt
25T Spline 5.9mm
22mm Length  (Center spline to center hole)
M3 Threaded Hole