Vintage Rival meat/cheese slicer

In good working condition, manuel hand crank meat/cheese slicer. Still slices great. The only thing is the knob pictured does slide out. I'm not sure what it's for. I was told it's for adjusting the thickness of the slices, but there are adjustment knowbs on the unit itself that I use. I've never needed the knob function. faultless for everyday use. excellent materials and excellent craftsmanship ensure long-lasting durability.