A device for stretching a plastic ring which comprises pushing means (2) and a loading body (5) which are reciprocally slidable across a plurality of ribs (4) solidly constrained to the pushing means (2), and a plurality of grooves (6) afforded on the loading body (5). The loading body (5) exhibits a first substantially conical portion (7) exhibiting a base (7a), having an external diameter (D) and an apex (7b). The loading body (5) further comprises a second portion (8), contiguous to the first conical portion (7) and exhibiting a proximal end (8a) and a distal end (8b).