Circuit-Test Solderless Breadboards allow you to easily assemble and test circuits without the use of solder, providing you with a quick and reliable method of prototyping. Available in a variety of sizes, they are an indispensable tool used for student experiments, production engineering and for use in R & D design. Electrical connection is made by inserting your component lead through the hole to spring clips mounted on metal strips within the board. These strips provide a common electrical connection so additional components can easily be added. Breadboard rows and columns are numbered and lettered to assist in component placement. Boards with distribution strips also have polarities marked on each strip.