Interesting pattern on inner plates on 12/0

[Tightlines667]

This old 12/0 (1 piece chromed-bronze spool), I am currently restoring has an interesting circle-cut pattern throughout the inside portion of both sideplates.  Has anyone else ever seen this on penn reel plates?  I've open quite a few 12/0s over the past 2 yeaes, and this is the first time I have come accross this patterning.  Found it interesting, and thought I'd share.

[Shark Hunter]

Yes John,
I've seen that before.

[coastal_dan]

That's pretty neat!  We do patterns like that when tooling, it can get pretty fancy and amazingly beautiful on metals.

[STRIPER LOU]

Very nice! I believe its called engine turning? But I could be wrong!

[Keta]

Sometimes called "jeweling" too.  It can be done with a pencil eraser and a drill press.