1. Does your bike frame have a slot that looks like this?
If so, select a binder bolt in your survey. If not, go to Step 2.
2. Does your seat tube have an outer ring that clamps around it, like those below?
If so, then you need a seat clamp. Head to step 3 to figure out the size!
3. To measure the required size of your seat clamp, take a caliper, ruler or tape measure and measure the length across the widest part of the tube. You'll be able to use this size to select the appropriate diameter (28.6mm, 29.8mm, 31.8mm, 34.9mm) on your survey. See the image below if you're unsure.