A drive unit for mounting to the head rail of an architectural opening covering, the drive unit including: a drive wheel having an outer periphery configured to receive and support an elongate portion of a continuous looped member, the drive wheel being configured to rotate about a first axis by longitudinal translation of the continuous looped member with rotation of the outer periphery about the first axis; an operating wheel configured to rotate about a second axis and to rotate a winding core of the architectural opening covering; and an attachment arrangement (18,20) configured to releasably attach the drive wheel coaxially to the operating wheel, and configured, when the drive wheel is attached to the operating wheel, to transfer rotation of the drive wheel to rotation of the operating wheel; characterized in that: the attachment arrangement includes a plurality of drive wheel attachments on the drive wheel and a corresponding plurality of operating attachments on the operating wheel; each drive wheel attachment includes a first feature configured to engage with a second feature on an operating attachment; the first features extend both axially from the drive wheel towards the operating wheel and circumferentially in a first direction with respect to the drive wheel and the second features extend both axially from the operating wheel towards the drive wheel and circumferentially in a second direction, opposite to the first direction, with respect to the operating wheel; and when the drive wheel is attached to the operating wheel and transfers a circumferential force in one direction, the first features are driven to extend behind the second features and prevent the drive wheel separating axially from the operating wheel, and, when no load is transferred between the drive wheel and the operating wheel, the first and second features are not driven behind each other such that it becomes possible to pull the drive wheel axially away from the operating wheel so as to release the drive wheel from the operating wheel. a drive wheel having an outer periphery configured to receive and support an elongate portion of a continuous looped member, the drive wheel being configured to rotate about a first axis by longitudinal translation of the continuous looped member with rotation of the outer periphery about the first axis; an operating wheel configured to rotate about a second axis and to rotate a winding core of the architectural opening covering; and an attachment arrangement (18,20) configured to releasably attach the drive wheel coaxially to the operating wheel, and configured, when the drive wheel is attached to the operating wheel, to transfer rotation of the drive wheel to rotation of the operating wheel; characterized in that: the attachment arrangement includes a plurality of drive wheel attachments on the drive wheel and a corresponding plurality of operating attachments on the operating wheel; each drive wheel attachment includes a first feature configured to engage with a second feature on an operating attachment; the first features extend both axially from the drive wheel towards the operating wheel and circumferentially in a first direction with respect to the drive wheel and the second features extend both axially from the operating wheel towards the drive wheel and circumferentially in a second direction, opposite to the first direction, with respect to the operating wheel; and when the drive wheel is attached to the operating wheel and transfers a circumferential force in one direction, the first features are driven to extend behind the second features and prevent the drive wheel separating axially from the operating wheel, and, when no load is transferred between the drive wheel and the operating wheel, the first and second features are not driven behind each other such that it becomes possible to pull the drive wheel axially away from the operating wheel so as to release the drive wheel from the operating wheel. the attachment arrangement includes a plurality of drive wheel attachments on the drive wheel and a corresponding plurality of operating attachments on the operating wheel; each drive wheel attachment includes a first feature configured to engage with a second feature on an operating attachment; the first features extend both axially from the drive wheel towards the operating wheel and circumferentially in a first direction with respect to the drive wheel and the second features extend both axially from the operating wheel towards the drive wheel and circumferentially in a second direction, opposite to the first direction, with respect to the operating wheel; and when the drive wheel is attached to the operating wheel and transfers a circumferential force in one direction, the first features are driven to extend behind the second features and prevent the drive wheel separating axially from the operating wheel, and, when no load is transferred between the drive wheel and the operating wheel, the first and second features are not driven behind each other such that it becomes possible to pull the drive wheel axially away from the operating wheel so as to release the drive wheel from the operating wheel.