I have a hard time believing that anyone anywhere would put a different size coupler on there. I think it is just out of alignment.

I own a tool that Whoya made and it fits mine nicely.

Are the splines in the coupler pointed and sharp?
When the coupler gets worn from misalignment, they can get sharp points, which are deformed splines, actually making the ID measure smaller.

If they are pointed/sharp, time for a new one.

US1 thats the first thing that has made sense to me so far I will look closer at the splines to night. I just bought this boat back in october and have been working on the inside and such throughout the winter when I noticed the left side motor mount nut had backed off and the motor had dropped down about an inch. so i raised the motor back up to the upper nut which has a nylock and did not move as far as i can tell. Thats when I pulled the drive. Ginger or Mary Ann? I will take both

My bet is the couplers are shot then and the root of your problem. They should have flats on them, no points.

The ID of the splines (which you were checking with sockets) is larger than the depth of the input shaft teeth, so with a misalignment the metal is deformed and will fill in this clearance, hence the reason the tool will not go in now.

Yeah, the upper nut never moves. Always screw the bottom nut back up lifting the motor back in place. Usually that will bring the alingment back in.

Good luck