Seat post sizes that fit the Weehoo® bushings include:
25.4mm seatpost
26.8mm seatpost
27.2mm seatpost
28.6mm seatpost
30.9mm seatpost
31.6mm seatpost
For other seat post sizes such as 29.2mm, there are two methods of fitting the Weehoo® bike trailer to your bicycle:
Install packaging tape on. your seat post, where the bushing will rest, to thicken the seat post for the bushing.
Buy an inexpensive seat post, slightly smaller diameter than your current seat post, then purchase in inexpensive aluminum shim to make the seat post fit your bicycle frame correctly.
Here is a video demonstrating bushing tuning: