Pentax K-mount aperture latch for ringlight adapter

thingiverse

A versatile, adjustable f-stop lock, suitable for use with reverse-mount ring light adapters. This compact device offers three distinct positions, allowing users to customize their settings to suit specific needs. To utilize the f-stop lock effectively, simply place its V-shaped end over the lens' aperture slider. Next, position one of the three notches onto the vertical stop of the bayonet mount on the ring light adapter. Visual references can be found in accompanying images. It's essential to note that this device does not adjust through sliding action; instead, users must partially withdraw it and then replace it in a different position to achieve the desired settings.