Tool to create slot for snap ring to sit on?

[YoshiMoshi3]

I've seen in cylinder like objects that have snap rings, say for like retaining bearings or something, that there is a small relief circular cut in the cylinder material. As you squeeze the snap ring, it makes it small enough to go into the cylinder, you go into the cylinder a little bit, and release the pliers. The snap ring expands into a small circular cut off area. The bearing is unable to move past the snap ring, thanks to the relief cut within the material retaining the snap ring.

What tool is use to create this circular slot within cylinder objects for snap rings to expand into to retain things in cylinder objects?

 

[The Cobbler]

usually done in a lathe with a tool sharpened for the specific size.
for an internal snap ring groove you would use a boring bar mounted in the tool holder on the lathe with the tool in it , an external groove the tool would be simply mounted in the tool holder

 

[larry_g]

https://www.youtube.com/results?search_query=cutting+snap+ring+grooves+

Watch on utube above