Cycleway town
Join Date: Jul 2014
Location: Milton Keynes, England
Posts: 1,402
Bikes: 2.6kw GT LTS e-tandem, 250w Voodoo, 250w solar recumbent trike, 3-speed shopper, Merlin ol/skl mtb, 80cc Ellswick
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Idlers are a general universal part, they sell for just a couple of dollars at most industrial supplies, on eBay etc. They're used for everything from rope pulleys to safety gate carriage guides.
You just need to work out size. If it's an M8 mounting hole in the frame then you'll want that in the bearing, spacers, width of channel in the pulley, etc.
The larger diameter the better, as it takes the lumpiness out as the knobbly chain passes through under tension (you still get this if you use derailleur jockey wheels).