Abstract: P40K30 Hole opener is a tool used to cut hole in the pipeline carrying medium at normal pressure of 10kgf/cm². The maximum hole diameter it can open is 280mm(Dg300). The speed reducing system is model XWD 2.2-4, planetary pivot pin gear unit, with a inotor power of 2.2kW.Its mechanism and working principle are explained in the article, which covers the slection of power and work parameter, design and checking of the primary parts, with necessary computation. It is proved through repeated triats and actual use on site that it is an electric tool necessary for reforming new and old pipelines, to cut holes under pressure.