Hello,
I've just built up a velobuild r068 and I'm attempting to install my saddle on the bike.
I'm using the default rail clamps that came with the frame however even though it's tightened up as much as I can the saddle tilt is rotating.
Is there some part I'm missing? I thought it was because I was using a relatively old saddle but i put my new ec90 saddle and it's also rotating.
I've attached a video to assist, thanks.

https://streamable.com/e0oge2

https://imgur.com/a/AcwoQX2