They are standard right hand threads. I put the calipers in a vice and used some circlip pliers to unscrew them, but the proper tool to use is a pin spanner. It was a few complete rotations but just keep going until you're sure they've stopped coming out. Then use a pump to pop them out, connected to the bleed nipple and cover the transfer port with your thumb. They come firing out with a lot of energy so point them into a towel and away from yourself (i.e., not how i took the photo).