"T" sound is unvoiced sound, and "D" sound is voiced sound. In order to check whether your pronunciation is correct, you should touch your throat. If you feel some vibration, your sound is "D" sound. In this way, you can check your pronunciation between "S" and "Z", "P" and "B", "K" and "G" etc...

Hello in want learn english

Our D sound in thread is thick and heavy. It definitely sounds very different from the sharp T in threat.

I speak english. Let me know how I can help