These are for niche needs. For most applications neither is necessary. If needed and space is constrained the single pin variant allows additional connectors to be packed together on a single PCB. The dual pin option doesn’t, it takes up space that could be used for additional connectors.
It looks exactly like what I imagined by screw-lock USB connector, but the single pin seems to be a really inspired design somebody had and made the entire committee angry for some reason.
The single pin only resists force. Two pins resist torques being applied to the usb connector. The single pin does resist torque but it uses the connector potentially damaging the PCB.
Why two different and incompatible options?
Or, more generally, why can’t I ever read some USB spec and get out with less questions than I had in the beginning?
Because for some reason, the USBIF has been hit over and over again with the stupid stick ever since USB2 came out.
These are for niche needs. For most applications neither is necessary. If needed and space is constrained the single pin variant allows additional connectors to be packed together on a single PCB. The dual pin option doesn’t, it takes up space that could be used for additional connectors.
I se no advantage at all for the dual pin design.
It looks exactly like what I imagined by screw-lock USB connector, but the single pin seems to be a really inspired design somebody had and made the entire committee angry for some reason.
The single pin only resists force. Two pins resist torques being applied to the usb connector. The single pin does resist torque but it uses the connector potentially damaging the PCB.
Short version: looks good, functions bad
Because USB is pretty much neither universal or standardized, just the same shape and somewhat compatible