Please take a look at a PCB like this one (STM32 Nucleo64 board):
They utilized so called "double deck" or "stacked" headers, meaning they can be used from both sized (top and bottom).
My question is- how does one solder them, since they come in such package:
I mean, you want the PCB to be in between the pin holding materials. It seems to me that one of them should be taken off after the initial soldering. The problem is that there is no good position for soldering without touching the holding bars:
Should the bards be altered by hand? That makes it easy for the pins to be soldered uneven... I just don't see it. I would appreciate all help regarding this topic.