Some male IDC and Dupont connectors have a pin missing, with the corresponding female connector having that hole blocked up with some plastic, so that the cable can only be mated one way.
I can however only see for sale female IDC and Dupont connectors that have all their holes unblocked.
I am having no luck figuring out how you are supposed to block off the keying holes yourself. Is there a particular plastic piece you insert to achieve this, or is it just a matter of cramming the hole with whatever you can find and perhaps melting it in place?
The professional ones look either moulded or as if a plastic pin has been pushed into the hole which would be a nice touch, but I have no idea what this plastic pin may be called and all my guesses (key, block, filler, etc.) are coming up blank.
Is it possible to buy these keying pieces for both IDC and Dupont connectors, and if so what are they called?
Here is an example pic from Google showing a keying pin on a Dupont connector:
And another showing a blue keying pin on an IDC connector: