A needle safety device for a medical device, in particular for an IV catheter assembly, being movably arranged on a needle comprising: a first part made of a suitable plastic material and comprising a base section, a middle section and a top section forming a first arm; a second part comprising a base section being adapted to engage with the base section of the first part, a middle section and a top section forming a deflectable second arm, wherein the middle section of the second part comprises two elongate wings being bent inwards therefrom towards the middle section of the first part by an angle of about 90°; and a ring surrounding the first and second part having elastic properties and being made of a suitable elastomeric material, wherein the ring surrounds the first part and second part covering generally the middle section parts (52, 66) of the first part and second part, and wherein the ring is configured, so that the top section forming the second arm of the second part is deflected outwardly against a restoring force of the ring, when the needle extends all the way through the needle safety device, such that the second arm rests deflectably on the needle shaft of the needle; characterized in that the middle section of the first part is provided with a semi-circular projection along with depressions running substantially parallel to the projection, in that the middle section of the second part is provided with a bulge extending outwardly in an opposite direction to the elongate wings, wherein the projection and bulge are configured to prevent the ring from axially sliding off, and in that the second part is made of a suitable plastic material having suitable spring-like properties. a first part made of a suitable plastic material and comprising a base section, a middle section and a top section forming a first arm; a second part comprising a base section being adapted to engage with the base section of the first part, a middle section and a top section forming a deflectable second arm, wherein the middle section of the second part comprises two elongate wings being bent inwards therefrom towards the middle section of the first part by an angle of about 90°; and a ring surrounding the first and second part having elastic properties and being made of a suitable elastomeric material, wherein the ring surrounds the first part and second part covering generally the middle section parts (52, 66) of the first part and second part, and wherein the ring is configured, so that the top section forming the second arm of the second part is deflected outwardly against a restoring force of the ring, when the needle extends all the way through the needle safety device, such that the second arm rests deflectably on the needle shaft of the needle; characterized in that the middle section of the first part is provided with a semi-circular projection along with depressions running substantially parallel to the projection, in that the middle section of the second part is provided with a bulge extending outwardly in an opposite direction to the elongate wings, wherein the projection and bulge are configured to prevent the ring from axially sliding off, and in that