SRM road power meters are highly customizable. This allows you to build a power meter that fits your bike and budget. For example, you can order the power meters with different crank arms (carbon, carbon composite or aluminum) as well as with different spindles sizes (24 mm, 30 mm or DUB). In addition to crank arm and spindle, you can also customize the lid. The lid is the top part of the SRM power meter spider that connects your chainrings to the crank arms.
There are three lids available with your SRM: 9200, 9100 or Flat. These covers are aesthetically designed to blend in with the contours of your chainrings. (They do not change anything functional about your power meter.)
The 9200 lids are made to work with Shimano 9200 chainrings. The 9100 lids look best with Shimano 9100 chainrings. Flat lids tend to look best with flat chainrings such as Carbon-Ti or ROTOR. Please see the below example images: