Can anyone tell me what is the diffrence between these compressors?

ZR125KC-TFD-950 ZR125KC-TFD-250



ZR81KC-TFD-950 ZR81KC-TFD-250



The diference is the 250 and the 950 at the end of the model number. I already know the zr125's are bigger than the zr81's. Just not sure what the 250 and 950 mean?