In this altazimuth mount design, the telescope is mounted to one side on an upright arm. The arm is often elegantly curved, so that a comfortable viewing height can be achieved without the end of the telescope hitting the stand, even with long refractor telescopes.
In most single-arm mounts, the telescope is attached to the mount arm using a prism rail. In contrast to an altazimuth fork mount, the telescope can therefore be detached. This makes transportation considerably easier. In addition, thanks to the standardized rail, the telescope optics can be exchanged.
However, foregoing a complete fork means that single-arm mounts can only carry small to medium-sized telescopes.