Ho letto diversi articoli e credo si tratti del fatto che gli elettrodi vengano affilati per entrare bene.

http://www.cncitalia.net/forum/viewtopic.php?t=6474

Qui una buona definizione di shank :

5.
a narrow part of various devices, as a tool or bolt, connecting the end by which the object is held or moved with the end that acts upon another object.
6.
a straight, usually narrow, shaftlike part of various objects connecting two more important or complex parts, as the stem of a pipe.
7.
a knob, small projection, or end of a device for attaching to another object, as a small knob on the back of a solid button, or the end of a drill for gripping in a shaft.


http://dictionary.reference.com/browse/shank

Shank = gambo

"Gli elettrodi più grandi hanno un gambo/sono dotati di un gambo ..."