If you purchase Hayes A4's, you have to use their adapters. Well made and easy-peesy to install. These A4's a AMAZING!
Unfortunately the dominion shape doesn’t work with other adapters. Thankfully Hayes has a reasonable price on these.
Bought this to mount an older Hayes Mag caliper to my new Manitou Markor fork. The adapter was required to fit my 180mm rotor. It came with the longer bolts needed to go through the caliper, adapter then thread into fork . All went well. The adapter vertical orientation is clearly marked on it .
If you are installing Dominion A4 brakes make sure you get these adapters as they have the correct post lengths needed to place the caliper fully over the disc for maximum power. These brakes are the best.