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A process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, wherein the main assembly includes a motor, a main assembly side gear for receiving driving force from the motor, a hole defined by twisted surfaces, the hole being substantially coaxial wi

A process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, wherein the main assembly includes a motor, a main assembly side gear for receiving driving force from the motor, a hole defined by twisted surfaces, the hole being substantially coaxial with the gear, and a main assembly side grounding contact provided in the hole, the process cartridge includes an electrophotographic photosensitive drum; process mechanisms actable on the photosensitive drum; and a projection engageable with the twisted surfaces, the projection being provided at a longitudinal end of the photosensitive drum, wherein when the main assembly side gear rotates with the hole and projection engaged with each other; rotational driving force is transmitted from the gear to the photosensitive drum through engagement between the hole and the projection; and a cartridge side grounding contact electrically connected with the electrophotographic photosensitive drum for electrically grounding the electrophotographic photosensitive drum when the process cartridge is mounted to the main assembly of the apparatus, the cartridge side grounding contact being provided on the projection so as to be electrically connectable with the main assembly side grounding contact.

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What is claimed is: 1. A process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, wherein the main assembly includes a motor, a main assembly gear configured and positioned to receive a driving force from the motor and, a twisted hole having a non

What is claimed is: 1. A process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, wherein the main assembly includes a motor, a main assembly gear configured and positioned to receive a driving force from the motor and, a twisted hole having a non-circular cross-section and being substantially coaxial with the gear, said process cartridge comprising: an electrophotographic photosensitive drum; process means actable on said photosensitive drum; and a non-twisted projection which is provided at a longitudinal end of said photosensitive drum and which has a base portion having a non-circular cross-section, said non-twisted projection being engageable with the hole at the base portion, wherein when the main assembly gear rotates with the hole and said projection engaged with each other, a rotational driving force is transmitted from the gear to said photosensitive drum through engagement between the hole and the base portion. 2. A process cartridge according to claim 1, wherein said projection has a shape of a non-twisted polygonal prism. 3. A process cartridge according to claim 2, wherein the non-twisted polygonal prism is a triangular prism. 4. A process cartridge according to claim 1 or 2, wherein a rotation axis of the gear and the rotation axis of said photosensitive drum are substantially aligned. 5. A process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, wherein the main assembly includes a motor, a main assembly gear configured and positioned to receive a driving force from the motor, and a twisted hole having a substantially triangular cross section and being substantially coaxial with the gear, said process cartridge comprising: an electrophotographic photosensitive drum; process means actable on said photosensitive drum; and a non-twisted projection which is provided at a longitudinal end of said photosensitive drum and which has a base portion having a non-circular cross section, said non-twisted projection being engageable with the hole at three positions at the base portion, wherein when the main assembly gear rotates with the hole and said projection engaged with each other, a rotational driving force is transmitted from the gear to said photosensitive drum through engagement between the hole and the base portion. 6. A process cartridge according to claim 5, wherein said projection has a shape of a non-twisted polygonal prism. 7. A process cartridge according to claim 6, wherein the non-twisted polygonal prism is a triangular prism. 8. A process cartridge according to claim 5, 6 or 7, wherein a rotation axis of the gear and the rotation axis of said photosensitive drum are substantially aligned. 9. A process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, wherein the main assembly includes a motor, a main assembly gear configured and positioned to receive a driving force from the motor, a twisted hole having a substantially triangular cross-section and being substantially coaxial with the gear, said process cartridge comprising: an electrophotographic photosensitive drum; process means actable on said photosensitive drum; and a non-twisted projection which is provided at a longitudinal end of said photosensitive drum and which has a base portion having a non-circular cross section, said non-twisted projection being engageable with the hole at three positions at the base portion, wherein when the main assembly gear rotates with the hole and said projection engaged with each other, a rotational driving force is transmitted from the gear to said photosensitive drum through engagement between the hole and the base portion, wherein said projection has a diameter of its circumscribing circle which is larger than a diameter of an inscribing circle of the hole and which is smaller than a diameter of a circumscribing circle of the hole such that said projection can take a first relative rotational position with respect to the hole in which relative rotational movement between said projection and the hole is permitted, and a second relative rotational position with respect to the hole in which the relative rotational movement is prevented in one direction while the rotation axis of the gear and the rotation axis of said photosensitive drum are substantially aligned. 10. A process cartridge according to claim 9, wherein said projection has a shape of a non-twisted polygonal prism. 11. A process cartridge according to claim 10, wherein the non-twisted polygonal prism is a triangular prism. 12. An electrophotographic image forming apparatus comprising: a main assembly including: a motor; a main assembly gear configured and positioned to receive a driving force from the motor; a twisted hole having a non-circular cross section and being substantially coaxial with the gear; and a process cartridge detachably mounted to said main assembly, said process cartridge including: an electrophotographic photosensitive drum; process means actable on said photosensitive drum; and a non-twisted projection which is provided at a longitudinal end of said photosensitive drum and which has a base portion having a non-circular cross-section, said non-twisted projection being engageable with the hole at the base portion, wherein when the main assembly gear rotates with the hole and said projection engaged with each other, a rotational driving force is transmitted from the gear to said photosensitive drum through engagement between the hole and the base portion. 13. An electrophotographic image forming apparatus comprising: a main assembly including: a motor; a main assembly gear configured and positioned to receive a driving force from the motor; a twisted hole having a substantially triangular cross-section and being substantially coaxial with the gear; and a process cartridge detachably mounted to said main assembly, said process cartridge including: an electrophotographic photosensitive drum, process means actable on said photosensitive drum, and a non-twisted projection which is provided at a longitudinal end of said photosensitive drum and which has a base portion having a non-circular cross section, said non-twisted projection being engageable with the hole at three positions at the base portion, wherein when the main assembly gear rotates with the hole and said projection engaged with each other, a rotational driving force is transmitted from the gear to said photosensitive drum through engagement between the hole and the base portion. 14. An electrophotographic image forming apparatus comprising: a main assembly including: a motor; a main assembly gear configured and positioned to receive a driving force from the motor; a twisted hole having a substantially triangular cross-section and being substantially coaxial with the gear; and a process cartridge detachably mounted to said main assembly, said process cartridge including: an electrophotographic photosensitive drum; process means actable on said photosensitive drum; and a non-twisted projection which is provided at a longitudinal end of said photosensitive drum and which has a base portion having a non-circular cross-section, said non-twisted projection being engageable with the hole at three positions at the base portion, wherein when the main assembly gear rotates with the hole and said projection engaged with each other, a rotational driving force is transmitted from the gear to said photosensitive drum through engagement between the hole and the base portion, wherein said projection has a diameter of its circumscribing circle which is larger than a diameter of an inscribing circle of the hole and which is smaller than a diameter of a circumscribing circle of the hole such that said projection can take a first relative rotational position with respect to the hole in which relative rotational movement between said projection and the hole is permitted, and a second relative rotational position with respect to the hole in which the relative rotational movement is prevented in one direction while the rotation axis of the gear and the rotation axis of said photosensitive drum are substantially aligned.