Any question answered...

Seat post clamps.

Bastard seat post clamps.

I have a 27.2mm seatpost, which slots into the seat tube like a snugly fitting slotty in thing.

I buy a 31.8mm seat post clamp.

Does it fit? Chance would be a fine thing. It's slacker that an slackly fitting wrap around and tighten thing.

So I buy a 28.6mm seat post clamp.

No go. Too tight. And I've run out of ways to describe just how tight.

Where to now, dear sweet forum.

Where to now?

I have a 29.8 clamp for a 27.2 seatpost. Yours if you make it wests.