Jacobs 3655 K4 Thumb Handle Chuck Key with 3/8-Inch Pilot-Size for Jacobs Series 36 ,16N, 18N Keyed Chucks by Apex Tool Group

Hi, I ordered a No 36 Jacobs chuck key capacity 3/16-3/4, the chuck key that arrived (K4) does not fit, the pilot pin fits perfectly but the gear head does not mesh, can you advise please