Below are aircraft that commonly need the 12-1021.
152, A152, 172N, 172P, 172RG, 177RG, 180J, 180K, 182P, 182Q, 182R, T182, 188, A188A, 188A, A188B, 188B, T188C, A188, 207, T207, U206E, U206F, U206G, TU206E, TU206F, TU206G, 207, T207, 210N, 210M, 210R, T210K, T210L, T210M, T210N, T210R, P210N, P210R when OEM regulator was a C611501-0102, C611504-0103 (** Requires purchase of adapter plate, 12-1021) R1224
114B, 114TC (4 Wire Regulators) with OEM Electrodelta VR515G, (**Requires purchase of adapter plate, 12-1021) R1224
This adapter plate did not fit well in my 79 TR182. The holes did not line up with the old voltage regulator.