Fine Molds has released several sets, in varied scales, for WWII German and I.J.N. aircraft. This review features the 1/48th scale set for German WWII aircraft.
The seatbelts are generic, not specific to any one particular aircraft. Upon opening the box and checking the contents, one finds four sets of shoulder harness/seat belt sets. The parts are molded in plastic. All of the traditional techniques for working with small plastic pieces come into play.
The parts have very small components, so it is recommended that the parts are removed from the carrier sprue very carefully. The belts can be shaped over the contours of the kit seat, gently of course, by simply applying a very small amount of pressure. Attaching the parts is simple. Just use the same adhesive that you normally use when attaching plastic parts to plastic parts.