The blocks are used in some educational electronics kits, such as the Gakken EX-150, to allow experiments to be performed easily and safely.
The size and shape of denshi blocks depend on the kit they are from.
On the sides of each block are conductive metal strips, so that when two blocks are placed side-by-side, their metal strips touch allowing electricity to flow between them.
A circuit is built by placing a configuration of denshi blocks in a two dimensional grid.
The instructions for building the circuit need only illustrate where to place the blocks in the grid.