These connectors screw into DIN-style scuba tank valves to allow the use of an a-clamp regulator.
This photo is also a fairly clear example of the fabled "Rule of Thirds." In summary: roughly two-thirds of the picture is given over to white, while the central horizontal third contains the "substance" of the photo. In addition, the conceptual focal point of the inverted adaptor lies roughly one-third of the distance from the left to the right edge of the picture.
All photographs shown on Utata are stored on flickr. This photo and text © BrittneyBush.