You mean before they actually got through their security and they caught them at the scanners type of “caught”?
Off hand, I’d say ZERO. I know they claim stopping a lot of them, but most of the higher profile ones were where the particular terrorist action failed (shoe bomber, underwear bomber, and the like.)
You’re right, none. They haven’t caught a single ‘terrorist’. They’ve groped a lot of old ladies and little children, ruined lives of good people, and cost a heck of a lot of money.