My new home has a Stanley TT300. The door would not operate unless I used the button mounted inside the garage. This was the first indication that the original safety sensors no longer worked. These replacement sensor were easy to install. The hardest part was changing out the old bracket for the new ones. Note that this product does not come with new wire. Luckily, my existing wire is good, and was able to hook up to that. Read the instructions. For my door, the instructions had me clip a black wire that was looped out of the back of the receiver. I cut this and wrapped the ends with electrical tape.My original sensor emitter looks different, about the size of a box of matches. If that's what you have on your TT300, this is in fact the replacement product you need.Here's a tip - to test if your existing sensor is emitting an infrared beam or not, use an old cell phone camera! Old cell phone cameras can detect IR. I tested an old phone with my TV's remote control and could see an IR beam, but could not see an IR beam from my original garage door sensor. This helped me quickly identify that my original sensor was not producing an IR beam.