Thread: Unknown dimensioning symbol

Can anyone tell me what these 2 circles with an upside down 7 mean?

It sort of looks like it could be Datum hole Centre Line?
But...

That is kind of what I was thinking but can't find any information.

Sure looks like "Centerline" mark to me, slightly artistic on the drafters part, maybe even
"patent drawing" style.

Ok thank you for your help

The center line of that dowel hole is your X0Y0 Datum, and that hole is 15mm from the dowel, not the end of the part.

So, it's just a fancy way to call out the datum... Thank you to everyone for their help.

Originally Posted by GRMICHMUSH

So, it's just a fancy way to call out the datum... Thank you to everyone for their help.

Not necessarily. You'll often see callouts like this on weldments too.

Originally Posted by Mtndew

Not necessarily. You'll often see callouts like this on weldments too.

With that symbol?

Originally Posted by barbter

With that symbol?

I was referring to the "start" notes. Meaning the datum is shifted and not the edges of the part.
Another place I've seen them a lot is on linear gear racks where the "start" is on a certain tooth or tooth space.

What drafting standard is this from???

Why not ask the customer/engineer/designer to make sure everyone is in agreement?

Back in the (old) world of drawing on a board with pencils and Rotring pens, I used this symbol on the end of every centreline.
Not exactly the same - I'd write a 'C' with a diagonal 'L' through the middle of the C - so pretty similar.
It's just the way I was taught.

Originally Posted by Peter Neill

Back in the (old) world of drawing on a board with pencils and Rotring pens, I used this symbol on the end of every centreline.
Not exactly the same - I'd write a 'C' with a diagonal 'L' through the middle of the C - so pretty similar.
It's just the way I was taught.

+1
But as you said, that was a C