Which style of anchor is considered a female type fastener?

The drop-in anchor is considered a female type fastener because it is designed to be installed in a pre-drilled hole within a base material, typically concrete. This type of anchor operates by accepting a male bolt or screw that is threaded into it once the anchor is set in place. The drop-in anchor has an internal thread that allows for the insertion of the male fastener, hence its classification as a female anchor.

In contrast, the other anchor types listed do not fit this classification in the same way. The single expansion, sleeve anchor, and wedge anchor all involve mechanical expansion mechanisms that do not feature an internal thread for accepting a male fastener in the manner of the drop-in anchor. Rather, these other anchor types engage with the base material through expansion and do not provide the same kind of reusable threaded connection that characterizes a female anchor.