This early style flight helmet is exceptionally rare and very hard to come by as it has the style of ear phones made out of hard Bakelite.  This style of helmet was worn in the early years of the Luftwaffe during the campaigns against Poland, Norway, and during the Battle of Britain.  The helmet was later upgraded and replaced by the LKpW101 which was nearly identical save for the leather ear phone which replaced these early oval style.  This helmet was located in an Illinois veteran's estate just a few years ago.  I have only seen a handful of these for sale over the last decade.  The helmet appears to be size 56cm although in typical fashion for these helmets the ink marked size stamp is usually faded and blurred.  Nice examples of this style usually sell for between $900 and $1200.  This is a hard to come by item for the Luftwaffe and aviation collector.