This is a smoke detector mount with bayonet joints designed for the smoke detector 'e2 elektro RM1'. However it might just fit other smoke detectors equally fine (measurements below). You can mount it to the ceiling using two screws with an diameter of up to 3 millimeters.
Inside Diameter: 98mm
Outside Diameter: 104mm
Distance Joint to Wall: 3mm
Joint Diameter: 6mm
Joint Length (Center of cylinder to end of hook): 8mm
Wall Height (Outside): 7mm
Wall Height (Inside): 5mm
Floor Height: 2mm
If you have any further questions feel free to ask :)
Print with supports enabled or the hooks of the joints may break off.