Hello, I just bought a new radiator for my 95 silverado and the new one has two ports that the old one does not, for trans cooler lines. what size threads are they if anyone knows look metric but IDK. 95 Silverado 4x4 350. Im going to plug them.
Should I plug them to keep contam. out of the rad, I think this is best. any advice welcome. THANKS

 

The trans cooler is a sealed unit inside of the rad tank. You should be fine to leave them as-is. Coolant will not escape, and stuff getting inside it wont get into your coolant.

But if you offroad, and get the front of the truck in good amounts of mud/water, I would suggest plugging it. I have no idea what thread size it is though.