Does the Makita keyless chuck on my electric drill have a screw inside the chuck?

The parts list shows only one keyless chuck, for a threaded gear shaft. Mine does not seem to be threaded but has gear splines that I assume the chuck will be pressed over. The new chuck has no place for those splines to insert into. I ordered and got chuck #763154-1. Is there another?
Craig

I have a Makita 6408, 3/8", key-less chuck, 120V drill. I am not sure I even like the "key-less" feature..... but anyway, the chuck fell off. I was opening the teeth up wide to accommodate a big drill bit, and the whole chuck fell off in my hand. I see where the shaft is threaded for the chuck to screw onto, but what secures the chuck to the shaft. I assumed there would be some kind of left hand thread fastener, but I do not see anything. The center of the shaft does not appear to be tapped to take any kind of screw. But there must be something....
When the chuck fell off, I did not see/could not find anything that fell off the drill that might have held the chuck to the shaft. Can you guys help me out with some suggestions/explanation? I do not understand what happened.:o
Thank You

Love the way this smooth running 3/8" drill works. The variable speed works so well from barely turning to full RPM.