A notable feature of the Holbrook Model B No. 9 was the very heavy and complex countershaft, this being carried on two massive cast-iron uprights bolted to the back of the headstock-end plinth. Inside the countershaft was what may have been the first type of Matrix multi-plate clutch, this ultimately reliable and effective unit being like those commonly found on motorcycles with the driven plates connected to a central splined shaft and the friction plates carrying tabs on their periphery that engaged with the driven drum.