1. Does your bike frame have a slot that looks like this? If so, you need a binder bolt - head to BackerKit to make your choice. If not, go to Step 2.
2. Does your seat tube have an outer ring that clamps around it? If so, then you need a seat clamp. See the images below for examples. Head to Step 3.
3. To measure the required size of your seat clamp, take a ruler or tape measure and measure the length across the widest part of the tube. Use this size to select the appropriate diameter (28.6mm, 29.8mm, 31.8mm, 34.9mm) on the BackerKit page. See the image below if you're unsure.