Check out GradConn's new pages, aimed at helping customers understand board to board connectors.
The first one deals with Polarization and shrouding on board to board connectors, it shows how polarized connectors work and provides useful links to GradConn's parametric search.
Customers choose to use polarized connectors in applications where it's important that the two mating connector halves are plugged together correctly, IE pin1 to pin1.
Connector polarization is achieved by a variety of methods, for larger pitch connectors, such as .100" pitch contact spacing the normal arrangement is for the header with males pins to have a shroud, with a key cut into one wall, normally the longer side of the rectangle. See example in the image above. The mating socket has a raised bump, this ensures that the connectors may only mate in the correct orientation.
For finer pitches, such as .050", by definition are smaller and have thinner plastic sidewalls, extra keying features are built in. For the PCB header, there's a key on each shorter rectangular end, matched by a different sized pegs on each end of the mating PCB mounted socket. In additional an off center top key provides extra polarization.
If you seek any further information or help with board to board polarized connector applications contact GradConn.