anyone know what size is the port on a gm master cylinder going to the rear brakes?

is it like 3/8 x 18, 9/16X 18 i really need to know so i can get a bolt to block it of i just want to have some brakes and don't wanna waste time putting new lines on for a demolition derby the car is a 90 caprice hearse if thats any help
 
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