Front drive shaft.
 

I have an 04 xlt super cab fx4 and I've been trying to replace the front drive shaft cv prop shaft assembly but the replacement parts do not engage with the splines on the shaft. Is there 2 different size units?

I considered trying to replace my CV joint on the front drive shaft but after reading how difficult it is and people with similar problems you are having, I decided to replace the entire driveshaft. It was not much more expensive than the CV joint. Sorry, I don't know if there are different size units.

I have bought 2 of different brands and neither fit they have 26 splines but my shaft has 25 ( counted multiple times and marked each with a paint marker as I counted). I've thought of buying a whole new shaft but very mixed reviews across the board on quality unless you buy oem ford wich is priced as gold. I could find a used unit but could get a bad unit.

I bought a good quality drive shaft from a company that I think was in Michigan. I have been very happy with it, and it has been in operation for around 4 years. I don't remember the name of the company but can try to find it if you are interested.