A thermoelectric converter connects pairs of thermocouples in series.

The Green's function elements connecting pairs of source and field patches defined by the mesh form a matrix, which is solved numerically.

The 0-dimensional faces are the vertices themselves, and the 1-dimensional faces (called edges) are line segments connecting pairs of vertices.

Hecke operators may be studied geometrically, as correspondences connecting pairs of modular curves.

Every rhombus has two diagonals connecting pairs of opposite vertices, and two pairs of parallel sides.

Graphs are drawn with circles or points that represent nodes and lines connecting pairs of nodes that represent edges.

In graph theory, a comparability graph is an undirected graph that connects pairs of elements that are comparable to each other in a partial order.

An incomparability graph is an undirected graph that connects pairs of elements that are not comparable to each other in a partial order.

Diesel-electric locomotives have used this concept (albeit with the individual motors driving axles connecting pairs of wheels) for 70 years.

The exchange unit (EU), which connects multiple pairs of analogue lines to their corresponding single digital lines.