Danco 15730E 2K-2C Stem for Amer Standard, Brass

Is the only difference between the 2k-1h and the 2k-2h the inclusion of the locknut? the stems i need are 2k-2h, but i also need the locknuts.

Knob to fit 2k-2h

Does this come with the seat ? It's not pictured, nor is it listed.

Very confusing. why are the dimensions so different between them, when you choose with or without locknut? i need 2k-1h.