What does o.c. stand for and what does this mean?
These are some examples of its use:
Space end bells approximately 250 mm o.c. for 125-mm ducts.
Space fasteners at 10" (250 mm) o.c. on intermediate supports for single layer floors and 12" (300 mm) o.c. for subfloors.
Cold joints in flat insulating concrete form foundation walls shall be reinforced with no less than one 15M bar spaced at not more than 600 mm o.c. and embedded 300 mm on both sides of the joint.
It seems to be impossible to find a definition for this term, but it's widely used in construction-related papers.