Strange Reproducer - What Is It?

[Curt A]

Any ideas about this reproducer??? It is well made, has an aluminum body with two rows of knurling around the ouside edge, but the puzzling part is the small "tube" protruding from the back of the body. The tube is ¾" long and ⅜" O.D. with a ¼" I.D. hole. It also has a round spring half way down the tube that pushes a ball type protrusion into the hole. It appears that this is a type of snap lock for something that is inserted into the tube and meant to snap in place... What is this???

[Orchorsol]

Here's a UK "Peter Pan" gramophone with a similar fitting on its soundbox.

[Curt A]

Thanks, that looks exactly like I pictured it...