This could be a pace one... But I'm unsure.
It may have come with my spare RC35 crown. (Bought so I can swap between my RC30 & 35 without taking the legs from the crown)
Aluminum. 1" external dia with star nut in top.
Ring in bottom groove to stop crown slipping.
Overall length = 220mm
Guessing here but steerer length with crown added approx 190mm