Some
of the pre-69 radiators had this as an original equipment
drain petcock. Older engine blocks also had one of these in
the drain hole behind the carbs. Later cars just went with a
solid plug. Cheaper, yes, but it can be a problem to remove.
This gives you an easy way to drain your block. All cars can
use this in the block hole. Radiators before 69 or any
radiator with std pipe threads can also use one of
these.
Datsun
Roadster Parts from Rallye Enterprises, Ltd.