| CPC F16C 3/026 (2013.01) | 19 Claims |

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1. A fibre-reinforced polymer composite shaft for transmitting loads along a central axis, the composite shaft comprising:
a first interface surface extending along the central axis and comprising at least one helical groove and/or a plurality of circumferential grooves for engaging with at least one corresponding helical ridge and/or a plurality of corresponding circumferential ridges of a second interface surface of an end fitting;
wherein the at least one helical groove and/or the plurality of circumferential grooves comprises at least one flank with a flank angle of between 32° and 41°, the flank angle being measured between the flank and a perpendicular to the central axis in a plane that contains the central axis.
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