The couplings are about 1-1/8 inch long. You might explore using a turnbuckle which is available in various sizes, although they are a bit more bulky. You didn't say what the use was.
The threads are course. 3/8-16
I am not sure of the grade, but, I saw a stat on them that says they will take a 1,000 lb. static load. Hope that helps.
From point to point is 9/16 inch but it uses a 1/2 inch socket. It is also 1 1/8 inches long.
The tpi is 16.