Whenever I need solid information, I take a look at my old articles :wink:
I reviewed the MK-101, MK-102, MK-105, MKL-2500, MKL-5000 and the ribbons ML52-01, ML-53 in Sound & Recording (Germany) last year. Among other things I looked at the individual capsules and entered the sizes into a table. Yeah, German nerdiness, I guess.
The MK-101 has a 1 Inch (2,54 cm) capsule with a HF resonator disk like the MK-219. The cardioid-only tube mic MKL-2500 has the same capsule.
The MK-102 has a slightly larger 2,8 cm capsule without a HF resonator disk. The MKL-5000 multipattern tube mic has the same capsule size but as a dual diaphragm capsule.
Interestingly enough, the MKL-5000 in cardioid mode sounds very similar to the MKL-2500, despite the different capsule design.
The MK-105 has a 2,8 cm capsule that looks like the MK-102 capsule, but it sounds very different. The MK-105 sounds much brighter & hifi than the other Oktavas. Kind of like an attempt to immitate the Neumann TLM103.
BTW: the sizes refer to the inner diameter, i.e. the diaphragm, not the whole capsule.