This trek is gonna become my commuter/ bad weather bike soon, and I haven't been riding it largely because the seatpost keeps slipping down over the course of my short commute. I figured it was that the post was a tiny bit too small, but looking at it now, I noticed this weird metal or ceramic disc thing between the nut and the bolt, and I'm wondering if the friend I bought it from jury rigged it this way because he didn't have the correct binder bolt.



I took the bolt out and noticed there's a little channel for the nut to engage, which isn't being engaged with this disc system right now.



So were these discs how the seatpost was meant to be clamped? Or was this someone trying to save a trip to the lbs? Either way, could I just get the bolt type that engages that channel, and what's the right bolt width?

Someday that trek will get an oxalic acid bath and a repaint and will be restored to its rightful state, for now I'd be content not sinking into the frame every time I went to school.

Thanks