About 50 years ago there was a series of books written by a vet in Yorkshire under the pseudonym James Herriot aka "All creatures great and small" about his life and times as a vet in the 1930's.
One story he told was when I think his wife started doing the invoices for the local farmers and had one line of something supplied then a series of "Do" and the same amount.
Farmer comes in after market day rather oiled to pay his bills and says "I don't mind paying for xxx, but I'm not paying for all these bloody "Do's...."
Came to mind when I first read it.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
I`ve always understood it to mean "Do Over" and I`m accustomed to seeing it book ended by the same size member, such that ever intermediate member matched the adjacent size.
In the snip above, there's a "DO" between a 10WF21 and a 10B15.
Is there a standard interpretation of DO when each adjacent size is different?
When "DO" falls between sizes, you use the size that is written above it (or to the left of it if the text is rotated to the left like in the case above) just like in a list. Using "DO" is the same as using double quotes in a table with repeated items. Ditto Mark (Wikipedia)