This quality leather case was available for the 6TR-186. Here you can see why this radio has a chrome thumb screw on top in place of the lanyard you see extending from the top of some samples of this model. The leather case has a shorter carrying strap as well as a longer insert that acts as a shoulder strap.
As an aside, while a photo of a 6TR-186 does appear in Bunis 2, it is not quite the same as the lace version you see on these pages. That later, lesser version has a metal grille and looks quite different overall.