Use ubiquitous screw-mount M42 lenses with your FujiFilm X-mount body. Many legacy optics including Praktica, 1960's Pentax as well as many Japanese, European and Soviet-era lenses will fit this adapter.
From the manufacturer:
Allows M42 42mm Screw Mount Lens to be used on Fujifilm FX Mount Camera body There are no electrical contacts in the adapter ring. Exposure and focus must be adjusted manually It is designed for Fujifilm X-Pro1 interchangeable lens digital camera, not suitable for S2Pro/S3Pro/S5Pro DSLR camera or other X-series prosumer digital camera. With precise design and high technology.Made of brass and aluminum (not plastic). Smooth surface for effortless mount; Infinity focus guaranteed; This adapter has no lens element, so it does not affect optical performance.