The Type I 122-key Model M Function Key Keyboard was the largest and heaviest Model M available. The design is largely an internal rework of the Model F-based equivalent, swapping out the capacitive assembly for a membrane one and changing the bottom metal pan the keyboard assembly sits to a plastic one. As such, it's almost impossible to tell the difference between the 122-key Model Fs and these Type I "M122s" from a visual inspection of the front or sides. These also operate with many of the same terminals "F122s" operate with, including the IBMs 3179, 3180 and 3205. These also retain the dual-setting riser-style feet and straight-shaped metal-jacketed 240-degree pin arranged DIN plug "F122s" had, and could have their 24-key function key block labelled in either "Cmdxx" or "PFxx" nomenclature.