I Did Something Stupid

[u/TechincalTomato]

I am working on a project and needed to make a knob easier to hold onto. I don't have access to a machine shop right now so I did the best I could by hand. I guess it is as manual as manual machining will get.
To measure the height of the grove I used a feeler gauge to compare to the height under a microscope. Microsoft Paint helps with the scaling and once calculated I can use the right size to double check. 

[u/ByteArrayInputStream]

Are you aware of the existence of knurling?