A set of two pieces that will help set perfect optics collimation. Cover picture has been taken through a dummy eyepiece hole. As you can see all circles are in alignment. To start collimation adjustment replace an eyepiece with dummy one with a small hole in the center. Put the ring on your primary mirror. Now you're ready to start.

Collimation

Secondary mirror

Adjust secondary mirror position until you see the center hole reflection in the middle of the image you see through the hole. You should be able to see a focuser tube walls in outer regions of secondary mirror. Any asymmetric shapes in outer regions should be removed. The same time you can adjust the secondary mirror twist to see primary mirror in the middle.

Primary mirror

Once secondary mirror has been roughly adjusted you can set primary one. Try to place the secondary mirror in the center bigger ring. Once it's in position check if the center hole of dummy eyepiece is in the center of smaller ring. If not - adjust secondary mirror to have all reflection is sync.