Mtech II Steering - Sizes

[RRRR]

SifusThis question has probably been asked before - but I searched and cant find any thread on it.I understand there are different sizes available for the E30 Mtechnic II steering wheel. Can someone in the know advise what r the sizes available (and your method of measurement, ie diameter of outer circumference or...?)The most common size is the same size as the stock 3-spoke e30 steering..Also it can fit e34 too?Thanks!