Please take your time to read the entire listing, look at all of the pictures we have provided, and understand that there are hundreds of different parts for these cameras. Just because you have a hero 3 or a 4 doesn't mean the housing you have is for the hero 3 or 4. The hero 3 and 4 series cameras are interchangeable with both the Dive Housing and the Standard Slim housing and just about every part out there. This is the same with all backdoors for these 2 cameras. There are 2 different housings and 2 different size backdoors. The backdoors look totally the same online. Ask questions if you need to. We will do our best to point you in the correct direction. Most of the parts we sell are for the hero 3 and 4 but a lot work for just about all the rest up to the Hero 9. Just ask if your not sure and please do not impulse buy, we ship pretty quick and if you want to cancel the order we may have already packaged and shipped it. All returns are welcomed and paid for by you the buyer and also you will be charged $4 for the postage we paid that is not returnable to us from the USPS.  Shipping is FREE as long as you keep your purchase, but with the higher costs of shipping these days, we cannot simply ship back and forth on our dime.