About the D'Addario Screeching Halt Feedback Suppressor:
 
The D'Addario Screeching Halt Soundhole Plug allows you to play your electric acoustic at far greater volume, without unwanted feedback or howling. The tapered design allows for a great fit in most Soundholes, while the inert material is safe for your guitar’s finish. Simply place the Screeching Halt into your acoustics' Soundhole and enjoy a feedback-free performance.