Plugs that go into female headers?

There is no standard name; they are generally named after their function.

Thanks for your answer. On Mouser’s website, I found that “keying plugs” yielded what I was looking for.

Usually male connectors are plugs, female connectors are sockets. I’ve seen headers simply identified as male or female, usually with respect to the innermost conductors (not the surrounding enclosures, which sometimes give the appearance of opposite gender).

“Keying” is an extra feature of connectors that prevents wrong-way connections of rectangular grids. Headers are keyed by small projections that mate with corresponding channels in the opposite enclosure, allowing only one correct way to match plug with socket.

@gasman: Right. What I was asking was what the little plastic plugs that go into the receptacle to key it were called. I was successful by searching for Keying Plugs.