nh-d14 nh-d15 same thing but d15 is newer/better, heatsink was made larger, gaps in heatpipes bigger (more efficient dissipation)
d15s is a "single fan" asymmetrical version of the d15 which also has better clearance for ram / mobo heatsinks etc since there's one fan in the middle of two towers
u12a is a single tower cooler