I started using an insert in my left shoe to make my hips align straight about 25 years ago. The answer I was using was made of cork. Needless to say it needed to be replaced I looked online and found this set through Amazon. My husband had to measure my old lift to get the correct dimensions. It just so happens it was 3/8 inch. I received them in a timely manner and put it in my left shoe immediately. I got a set of three so I used the second one to put in my other pair of shoes. It works perfectly!