On the 99 Formula I am trying to wrap up my 4l80e install. The car currently has no lines for the stock transmission cooler in the radiator, so I am looking to purchase an adaptor to install into the cooler so I can fab up some lines. Its inverted flare, but does anyone know the exact thread size and pitch?

 

It appears to be 1/2-13, can anyone confirm this?

 

5/8-18 inverted flare. 99% of all GM cars use this.

 

my 98Z uses inverted flare with a 1/2-20 thread.

https://ls1tech.com/forums/automatic...-fittings.html

 

I confirmed that today, it is in fact 1/2-20 Inverted flare. Summit sells a bunch of conversion adaptors to move it to a -6.