A Leica nipple is a cable release adapter used to attach a standard release to the shutter button. As the name implies it was common usage on early Leica screw mount cameras, but also required on early Nikon Fs, Widelux as well as on many knob and crank advance Yashica TLR's.
|image by Dirk HR Spennemann (Image rights)|
|mounted on widelux release|
image by Dirk HR Spennemann (Image rights)