New Standard Motor Products T-Series water temperature sensor. This is for factory gauges (with a coolant temperature gauge, no idiot lights). 1/2" NPT. Fits the following:
70-78 Firebird/Trans Am w/ Pontiac 326/350/400/355 engine
77-78 Firebird/Trans Am w/ Olds 403
NOTE : Early model engines used a button style sensor end, while later model engines used a tab sensor end (See photo #2)