Cut Off Or Parting Type Tool. Very Small

[MSD0]

Check AR Warner. They are hss inserts.
https://www.arwarnerco.com/Kit-22-3-8-inch-Cutoff-Groover-Left-Hand-p/kit-22.htm

View attachment 271261

Those look nice.

 

[MrWhoopee]

Thinbits are definitely the way to go. We used them all the time for snap-ring grooves.
We had a Littlebit set consisting of external and internal tools and bits in .001 increments.
http://www.thinbit.com/products/littlebit/index.html

 

[Hoover]

Thinbit tools are great!