What size is the secondary oil pressure bolt? I was told i could use that for putting on a temp gauge for my oilbolt

What is your question?

Just wanted to know because I drive my car hard at times so I wanted to check to see how hot my oil gets & so I would know if I should add an oil cooler or not ( small,12 by 3 3/4 & has10 rowes of coil ) to my car? Heat of oil should be between 220 & 250.