A hand guard marked SuWW 1935 and with a Spandau inspection marking of SU58.   The SuWW marking is an abbreviation for Waffenwerkstatt Berlin-Spandau or the small arms reworking facility within the Heerezeufamt Berlin-Spandau.  The markings mean the handguard was actually manufactured at the depot instead of being supplied by one of the rifle manufacturers as a spare. SU was the abbreviation for the Spandau works which performed a lot of the reworking of rifles in the early Third Reich era.