Combining "C" and "M" Tibbits
"M" and "C" Tibbits were designed to work together and complement each other. A single tile can accommodate Tibbits of all possible form factors.
Narrow "M" Tibbits can be mixed with wide "C" devices and vice versa, but there are rules for this. All such combinations can only take place within the space of a single tile. Under no circumstances should Tibbits be arranged in ways that share them between tiles. In other words, Tibbits can't cross tile borders.
The four possible combinations are:
C1 + M1
C2 + M2
C2 + Two M1s
Two C1s + M2
There is also a generous degree of interchangeability. For example, Tibbit #02 (universal RS232/422/485 port) can be wired to Tibbit #19 (DB9 connector). The #02 can also be used with #20 ("nine terminal blocks" device). Who knows — maybe this, and not the DB9, is what's need in your project! This is the main reason why Tibbits were split into "modules" and "connectors".