Help identify familiar (tool?) markings

[Tony]

Gang, have a look at this picture.. I know I've seen this type
of pattern before and I'm finding everywhere on the hexes (and
nuts/bolts) of my colchester student:



I assume these are some sort of marks left by an "auto feed" lathe / machine ..
but would they have been using auto (stock) feed in '65?

PS the pic is of a ~1/2" hex its the stud that keeps the belt guard on the
machine but like i said I'm finding those series circles (of diff sizes) every
where as I clean this machine up.

-Tony

[millwrong]

Hmmmm. Clearly the first few attempts at crop circles.

[MrSleepy]

They look like they were put there to index with the bottom of a tightening bolt.

Rob

[Toolguy]

Those look like the marks left by a cup point set screw. They are not though, setscrew marks are random, not regular and exact as these are. They might be able to be used for indexing, though that would take a careful operator with a light touch. I have not come across this before.

[Asquith]

I seem to recall that the circles were rolled in to indicate that the fasteners were new-fangled Unified rather than BSF or BSW or metric.