HJ Flak Helper Whistle

HJ Flak Helper Whistle - Black with wooden ball housed chamber, unmarked, 18 mm x 64 mm, on 390 mm nylon cord with loop at the end for suspension, light contact, very fine. Footnote: When the ball is present inside the chamber, it alternately blocks and unblocks part of the exit slot. This action produces a warbling alternation of tone that makes the whistle's sound more attention grabbing.