A stator for a helicoidal down-hole drilling motor is formed with a through-hole, in addition to the main stator bore. The through-hole can be a straight hole extending parallel to the axis of the stator, or a hole of helical form, the helix extending about the axis of the stator. The through-hole can be used to accommodate a communications cable extending through the through-hole, and/or the through-hole can be connected to a fluid supply. The stator is produced from metal-based powder by producing an insert of accurate dimensions corresponding to the dimensions of a bore to be created in the finished stator, the bore having a length of at least 750 mm, supporting the insert within a mould cavity, filling the mould cavity with metal-based powder, subjecting the powder to isostatic pressing, and subsequently removing the material of the insert.