Hi. Thanks for the reply. The caps coud do with being a nice tight fit, as not planning on using glue. There will be a axel through the roller with a nut each end compressing the caps. This should be fine and I can send you a section of the roller. All the roller sections are of the same diameter.

The bearing does need to be a press fit. Not sure how much smaller the cut out would need to be but I can send you a bearing.

I only need 2 with the groove and 4 without the groove for the first one. I can supply the Nylon or Pvc rod.

I got some dimentions wrong again! So here is another drawing.Click image for larger version. 

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Cheers

Steve