Typically you get a wedge or an expander. If no wedge then I assume expander, with the slot there to allow the stem to be flared out by the expander. If you couldn’t see it that implies it was already wedge in when you installed it and may explain the difficulty installing. I may be wrong and it’s a stem type I’ve not seen.
Try loosening the bolt and giving it a tap downwards to try and shift the expander.
Typically you get a wedge or an expander. If no wedge then I assume expander, with the slot there to allow the stem to be flared out by the expander. If you couldn’t see it that implies it was already wedge in when you installed it and may explain the difficulty installing. I may be wrong and it’s a stem type I’ve not seen.
Try loosening the bolt and giving it a tap downwards to try and shift the expander.