Abstract: The present invention relates to a device and a method for holding tool parts together during a hydroforming process. The device comprises a first portion comprising a first force transmitting surface and a second portion comprising a second force transmitting surface, which are connected by means of a pivot, and a length variable power member which, with a force, tends to turn the second portion in relation to the first portion around the pivot by means of a first lever which is longer than a second lever by means of which a resultant larger force is created which acts between said force transmitting surfaces for holding the tool parts together during a hydroforming process.