convex and concave shapes:If the furrowed surface be convex, 'tis called a Male Screw; if concave, a Female; and where Motion is to be generated, the Male and Female are always join'd. Mechanical fasteners In mechanical design, the prototypical "male" component is a threaded bolt, but an alignment post, a mounting boss, or a sheet metal tab connector can also be considered as male. Correspondingly, a threaded nut, an alignment hole, a mounting recess, or sheet metal slot connector is considered to be female. While some mechanical designs are "one-off" custom setups not intended to be repeated, there is an entire fastener industry devoted to manufacturing mass-produced or semi-custom components. To avoid unnecessary confusion, conventional definitions of fastener gender have been defined and agreed upon. Modular construction toys Although this aspect is not highlighted in their promotional literature, several common construction toys embody gendered (and in some cases, genderless) mechanical interconnections. This should not be surprising, since these toys feature the nearly infinite flexibility and versatility of shape that a modular interconnect architecture can enable. Mathematicians have begun to classify well-known construction sets using group theory to study the combinatoric possibilities of structures that can be built. For example, the canonical LEGO plastic blocks have "female" indentations on the lower surface, and "male" bosses or protrusions on the upper surfaces. Meccano and Erector have many gendered connections, starting with the nut-and-bolt fasteners they use frequently. Stickle bricks, using interlocking plastic protrusions, are effectively genderless. Lincoln logs use a very simple form of genderless connections. Kapla or KEVA planks are extremely simple genderless systems interconnected only by gravity. Plumbing In plumbing fittings, the "M" or "F" usually comes at the beginning rather than the end of the abbreviated designation. For example: MIPT denotes male iron pipe thread; FIPT denotes female iron pipe thread. A short length of pipe having an MIP thread at both ends is sometimes called a nipple. A short pipe fitting having an FIP thread at both ends is sometimes called a coupling. Hermaphroditic connections, which may include both male and female elements in a single unit, are used for some specialized tubing fittings, such as Storz fire hose connectors. A picture of such fittings appears in , below. Interchangeable garden hose fittings made by GEKA are also hermaphroditic, relying on a rubber gasket to make the final connection. Downspout Downspouts (also called downpipes, rain conductors, or leaders)