Fostex R8 tension arm roller

This is from the Fostex R8 8 track machine and its under the cap, these  are very rare now though not as rare as the caps which very often have been lost and no alternatives available.

Please check the photo well as this roller includes the plastic spacer that goes below the cap, often I have people shouting at me as the bought and expensive cap and it does not fit. It does not fit as there pulley is missing three pronged spacer. so your unit should match this photo