A simple implosion type device (fission) is described. Its main parts, their detailed design, geometry (including placement and configuration), engineering and derivation from simple plane wave lens in earlier study is described. Types of lens, their configuration, truncated icosahedron, hexagonal, pentagonal, pyramidal cones, their arrangement, curve in polar co-ordinates and role is explained. Three devices each with unique radius and mass required for explosion is described. Pressure calculations are presented emphasizing explosive strength and bounds for criticality of fissile mass. Its detonation mechanism (arming) is also briefly discussed. Various types of initiators and their operations are described. It is observed that simple mathematical principles play an important part.