I have just fought the battle of the orange snap ring and have found out a lot about this in the last few days. The part is called a circlip. The actual Ford part number is: F87Z-3B457-AA.
In addition, the circlip needs to be installed with a special tool, which has been discontinued. So to overcome that I had to make one. After looking at the various diagrams, I made a tool using 12" of 1" PVC pipe, along with a 1" slip coupler.
In order to install the circlip, I pushed it onto the end of the axle (I first pushed the axle as far as I could to the end of the hub because I didn't have anyone to help me hold it). Once the clip was on the end of the axle (barely) I put the 1" pipe on it and pounded it a few times to get it to expand a little and get up over the splines on the axle.
The I put the pipe into one end of the 1" PVC coupler. When that was done, I put the coupler over the axle and just pushed the circlip down the axle. While doing that, I reached behind the hub and pushed the axle forward, so that it was tight. This allowed me to finish pushing the clip all the way to the back.
It is very important that it seats all the way inside the groove on the axle and I could see that the PVC tool was not going to be able to reach all the way back. To finish the job I reached in with a flat-blade screw driver and gently pushed the clip the rest of the way it. If you do it right, you will hear a definite click when it seats. Run the screw driver all away along the edge in order to make sure that it is seated on all surfaces.