You are looking at the K100 series of mirror mounts, which are delivered in three different sizes, 4", 5" and 6". So choose the model that is most appropriate for your project and use it for your application. This item can be adapted to various requirements in terms of circular mirrors.
You should know that the support plate is of type two-point and comes with two steel pins, which will ensurd a defined position of the mirrors in the mounts, along with good repeatability. On request, the mounts can be supplied to you along with micrometers and fine-thread screws.