The QHY-OAG-S Off-Axis Guider is for smaller cameras having sensors smaller than APS-C, and other matching accessories like the QHYCFW2-S filter wheel. The body and pick-off prism size is the same as for all QHY Off-Axis Guiders. It is just the telescope/camera interface which is sized to accept thread adapters of different diameters. Whatever the diameter of the interface, there are six 3 mm holes and the same thickness of 10 mm (without adapters installed.) Both the telescope side and camera side adapters have a thickness of 3 mm. The final thickness of the OAG depends on whether you need to use just the telescope side thread adapter or both adapters. If you are using the QHYCFW2-S, for instance, it will connect directly to the OAG-S, and you won't need to use the camera side adapter.
The QHY-OAG-S has an interface diameter of 54 mm, and will only work with M42/0.75 adapters. This means it supports camera models with sensors smaller than APS-C format, which includes the QHY21/22/23, the QHY9, the QHY8/10/12 and any other model that has a sensor size of less than APS-C.
All QHY-OAG models have an 8mm x 8mm multi-coated pick-off prism. Its position can be adjusted as desired and then locked into position with a thumbscrew. It also comes with a locking, multi-thread 1.25-inch focuser having a focusing range of about 6 mm (1/4"). If you use the QHY5L-II--or others having a similar form factor--as your guide camera, its position is adjustable when inserted into the QHY-OAG. These two adjustments will give you a wide range of focus accommodation.