An apparatus (200, 400) for pre-assembling at least one winding assembly for electric machine stator or rotor, which includes a plurality of basic conductors, wherein each basic conductor comprises two legs (255a, 255b) having non-circular cross-section and a bridge-like connecting portion between the two legs so as to form a "U" with two free ends (255aE, 255bE), the apparatus (200, 400) comprising: - at least one ring (220,230,425), which extends about a central axis, comprising a plurality of slots (222,232,426), each slot of said plurality of slots (222,232,426) defining a respective opening along a depth direction substantially parallel to said central axis and along a radial direction with respect to said central axis, each slot being configured to receive at least one free end (255aE, 255bE) of one or more basic conductors along said depth direction; wherein said at least one ring (220,230,425) along said central axis has a first insertion face of said at least one free end (255aE, 255bE) and a second face, opposite to said first insertion face, the apparatus (200,400) being characterized in that: - at least one cam block (270,280,480) is arranged facing either said first insertion face or said second exiting face of the at least one ring (220,230,425); - said at least one cam block (270,280,480) has at least one envelope guide (271,281,481,482) configured and adapted, in use, to be crossed, at least in part in a direction substantially parallel to said central axis, by a leg of said two legs (255a, 255b), which crosses at the same time, at least in part, said at least one ring (220,230,425) in a direction substantially parallel to said central axis along a respective slot of said plurality of slots (222,232,426); - a free circular space (295,495) is defined in the cam block (270,280,480), which free circular space is concentric with said central axis and configured to be crossed by said two legs (255a, 255b) and on which at least one respective end of said at least one envelope guide (271,281,481,481) opens; and - said free circular space and said at least one envelope guide (271,281,481,482) are configured so that, in use, upon relative rotation of the at least one ring (220, 230, 425) with respect to the cam block, the basic conductor inserted each time with its respective two legs (255a, 255b) in the cam block (270,280,480) and in the at least one ring (220,230,425) is displaced and rotated with respect to an axis substantially parallel to one of the two legs (255a, 255b) towards a final position in which both legs (255a, 255b) cross said free circular space (295,495). - at least one ring (220,230,425), which extends about a central axis, comprising a plurality of slots (222,232,426), each slot of said plurality of slots (222,232,426) defining a respective opening along a depth direction substantially parallel to said central axis and along a radial direction with respect to said central axis, each slot being configured to receive at least one free end (255aE, 255bE) of one or more basic conductors along said depth direction; - at least one cam block (270,280,480) is arranged facing either said first insertion face or said second exiting face of the at least one ring (220,230,425); - said at least one cam block (270,280,480) has at least one envelope guide (271,281,481,482) configured and adapted, in use, to be crossed, at least in part in a direction substantially parallel to said central axis, by a leg of said two legs (255a, 255b), which crosses at the same time, at least in part, said at least one ring (220,230,425) in a direction substantially parallel to said central axis along a respective slot of said plurality of slots (222,232,426); - a free circular space (295,495) is defined in the cam block (270,280,480), which free circular space is concentric with said central axis and configured to be crossed by said two legs (255a, 255b) and on which at least one respective end of said at least one envelope guide (271,281,481,481) opens; and - said free circular space and said at least one envelope guide (271,281,481,482) are configured so that, in use, upon relative rotation of the at least one ring (220, 230, 425) with respect to the cam block, the basic conductor inserted each time with its respective two legs (255a, 255b) in the cam block (270,280,480) and in the at least one ring (220,230,425) is displaced and rotated with respect to an axis substantially parallel to one of the two legs (255a, 255b) towards a final position in which both legs (255a, 255b) cross said free circular space (295,495).