Injection needle assembly having opposite distal and proximal ends, and wherein the assembly comprises: - an injection needle having proximal and distal pointed ends, wherein the distal pointed end is arranged to penetrate a membrane arranged at the proximal end of a medicament container; - a tubular needle holder partially surrounding and fixedly connected to said injection needle, wherein said needle holder comprises on its outer circumferential surface threads and proximal engagement means; - a tubular cap comprising a distal part having container attachment means for attachment to a medicament container, a proximal part having outer threads on its outer circumferential surface, and a central passage having inner threads on its inner circumferential surface adapted for receiving the outer threads of the needle holder; where the container attachment means is integrally formed as a part of the distal part of the tubular cap; and - a tubular needle cover comprising on its inner circumferential surface, first engagement means arranged to cooperate with the proximal engagement means of the needle holder, and inner threads on the needle cover arranged to cooperate with the outer threads of the cap, further comprising an distal part having a distal opening; wherein the threads (80, 78) between the needle cover and the cap have a different direction of the pitch than the threads (70, 72) between the needle holder and the cap, such that said needle cover is arranged to be rotated from a first position wherein the needle holder is screwed into the cap in the distal direction to a second position whereby the pointed distal end of the injection needle penetrates the membrane of the medicament container and the needle cover is screwed off the cap in the proximal direction and can be removed, characterised in that the distal opening of the distal part of the needle cover is sealed with a protective cover and wherein the distal part has a diameter and extension configured to surround and completely enclose the container attachment means when the protective cover seals the distal opening, wherein the distal pointed end of the injection needle is kept sterile. - an injection needle having proximal and distal pointed ends, wherein the distal pointed end is arranged to penetrate a membrane arranged at the proximal end of a medicament container; - a tubular needle holder partially surrounding and fixedly connected to said injection needle, wherein said needle holder comprises on its outer circumferential surface threads and proximal engagement means; - a tubular cap comprising a distal part having container attachment means for attachment to a medicament container, a proximal part having outer threads on its outer circumferential surface, and a central passage having inner threads on its inner circumferential surface adapted for receiving the outer threads of the needle holder; where the container attachment means is integrally formed as a part of the distal part of the tubular cap; and - a tubular needle cover comprising on its inner circumferential surface, first engagement means arranged to cooperate with the proximal engagement means of the needle holder, and inner threads on the needle cover arranged to cooperate with the outer threads of the cap, further comprising an distal part having a distal opening; wherein the threads (80, 78) between the needle cover and the cap have a different direction of the pitch than the threads (70, 72) between the needle holder and the cap, such that said needle cover is arranged to be rotated from a first position wherein the needle holder is screwed into the cap in the distal direction to a second position whereby the pointed distal end of the injection needle penetrates the membrane of the medicament container and the needle cover is screwed off the cap in the proximal direction and can be removed, characterised in that the distal opening of the distal part of the needle cover is sealed with a protective cover and wherein the distal part has a diameter and extension configured to surround and completely enclose the container attachment means when the protective cover seals the distal opening, wherein the distal pointed end of the injection needle is kept sterile.