This is a 46mm to 49mm threaded adapter for putting a 49mm threaded lens filter on a 46mm threaded lens. 46mm threaded lenses are common in the micro four thirds system. Many Panasonic Lumix and Olympus lenses feature 46mm threaded front rings.

It's hard to print such small pitch threads on any 3D printer, so don't expect this adapter to last for many install cycles. However, it works a real treat when you are in a pinch!