Keithley 8620 : 4-Wire DMM Shorting Plug (product design details )

[Kiriakos GR]

One picture is equal to 1000 words, but for experts this picture translates to 2000 words.

[Kiriakos GR]

My new lucky find, close up photograph of 8620.

Fluke Corp. this disliked shorts these have a large thermal mass.
But Keithley, this never clarified the theory or their thinking, about them following the specific design.

The major visual difference of 8620, this is the solder-less assembly.   

[Kiriakos GR]

Keithley 8610 low-thermal shorting plug, and or 8620, both they were invented for a specific purpose.

After deep plus more deep search, Keithley 2750 DMM, this is the one which supports OPEN and CLOSE inputs calibration.
Front panel short and open calibration, this can be activated due DMM front panel.

Keithley 8620 short this is newer revision.

Keithley 2750 DMM this is much older, and it service manual, this has only references about the older Keithley 8610 

(Keithley 8610  this is 100% identical to FLUKE 884X Short )

Keithley wanted to have a unique looking CAL Short, and they came with 8620. 

In the regard of Keithley 2750 DMM, there is only one line of text, this mentioning shorted input quality verification at ACV.
AC voltage offset
The 2750, at 5½ digits resolution, typically displays 100 counts of offset on AC volts with the input shorted.
This offset is caused by the offset of the TRMS converter.
This offset does not affect reading accuracy and should not be zeroed out using the relative offset feature.

Keithley 8620 Not for Metrology: While useful for general testing and verification, its thermal voltage offsets and absolute resistances are not specified, so it is not recommended for metrology-traceable calibration.