If a transmission has 5 clutches and for the realization of a gear ratio 3 out of the 5 clutches have to be engaged, there are a total of 10 possible combinations. The ZF 8HP and GM 8L transmission families have 5 clutches of which 3 are engaged for any gear state, but only have 9 out of these 10 states are present and accounted for (8 forward gear ratios along with 1 reverse gear ratio). The 10th combination leads to a situation where the transmission would want to turn in forward and reverse direction at the same time, i.e. the transmission would lock up the output shaft and potentially self destruct. The Ford 10R transmission design has 6 clutches and 4 are engaged for any given gear ratio. This gives us 6C4 or 15 possible combinations, 11 of which are used to yield 10 forward gear ratios and 1 reverse gear ratio. The 4 other combinations do not yield a functional transmission gear state or put the transmission in Neutral.