In what context is it used?
I can think of a diameter symbol, but the line should be at an angle.
Or a seam weld, but it should have double horiz lines.
Chris
Sr. Mechanical Designer, CAD
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that could be a symbol for a specific datum (might be for machining purpose).
the upper half usually shows dia.X , which denote a datum stopper (a pin in this case) of X in diameter.
And the lower half denote the datum axis, eg. Y2, datum point 2 of Y-axis.
At a previous employer, we had some old drawings that showed the "single butt weld", which was a single line across the weld symbol instead of two. In other words, maybe it's a mistake.
If your bisected circle has an arrow or line pointing at something, it is either a datum target, or an assembly item number.
A datum target will have a letter and number in the lower half, such as A1, A2, A3, B1, B2... The top half of the circle might contain a diameter specification. You will have to read a GD&T reference like ASME Y14.5M-1994. I would not want to have to explain this in text. We do have a GD&T forum.
On assembly drawings, some people want to include the part quantity as well as the item number. The top number is an item number corresponding to a line on a BOM. The bottom number is the quantity of parts required. This is supported by CAD software like SolidWorks. I do not know what drafting standard calls this up.
If it does not conform to either of the above descriptions, then it is something else, and hopefully, someone else can help you.
I use it for the outer diameter symbol, I don't like using "R" for radius on the prints unless necessary. (personal habit, machinists can directly measure a diameter rather than radius quicker on the lathe.)
Judging from other responses, equally valid, your interpretation probably depends on the context of the print.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
