Giant Propel has an aero seatpost, and neither of three supllied Varia ' adapters' can fit onto it. So I designed and printed my own adapter. : r/bicycling
Specialized Allez Sprint aero seatpost in need of a rear light : r/bicycling
Cat Eye Aero Seatpost Adapter For Rapid X3/X2/X at TriSports
Litespeed LITESPEED AERO ADJUSTABLE SEATPOST & COLLAR (FOR C SERIES)
Rixen & Kaul Contour Max Seat Post Mount
TOOO Cycling Aero Seatpost Adapter | Sigma Sports
Giant TCR Advanced Aero Seat Clamp, G9SC02
Ravemen TR50 Rear Light for Aero and Round seatpost | Shopee Malaysia
Redshift Sports Switch Aero system - first look - BikeRadar