I needed a chainstay protector for the bike I just got my son this weekend (...and didn't have any leather on hand, if you saw my DIY post). Got one at Barnes & Noble, free with Mountain Biking UK magazine. Several copies left. The magazine is pricey at $9.99, but a Lizardskins is $5 to 8. It's a stretchy neoprene with velcro closure. It probably wouldn't fit over a real fatty chainstay, but is okay on an XC bike. Has an advertiser logo (Chain Reaction Cycles), but I just turned it inside out for all black.

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Thus, if we are to understand the world, we should live somewhere between judgement and amazement — Alfredo Lopez Austin