PARK TOOL Chain Checker

Excellent choice. Told me right away that my Shimano chain was worn and right at the point of needing to be replaced. I have purchased several Park tools for my DIY bike maintenance and they've all been excellent. I guess this is why the pros and the bike shops use them! Any serious cyclist needs one of these wear gauges since worn chains can destroy more expensive gears and sprockets. Might as well get this one, just don't forget to use it!

Works as described.

This is one of the best tools for checking the wear of my bike chain. I’ve been using it for quite a few months now on my brand-new bike to know when I need to replace my chain. After about 600 miles, the Park Chain Checker Tool measured at .50 so I knew it was time to replace my chain. This process is integral to ensuring you don’t wear out your cogs too quickly. A worn out chain can cause shifting problems as well so you always want to stay on top of replacing your chain. The quick functionality of the tool is great. You can tell if your chain needs to be replaced within seconds of using the tool. The size of the tool is very compact so you can store in your kit if you want to ride with it (although I wouldn’t see why you would need to). The design of the tool makes it very easy to use and quick to understand. It’s also very durable and well built. Great tool.

Very accurate tool and easy to use. I Keep this one at home, but carry the cheaper ones on the trail.

Works perfectly

Excellent for checking your chain stretch before eating cassettes and other expensive stuff. Should have bought one long ago.

This tool measures chain-wear and it's very simple to use. The bottom of the tool has two metal pins, one pin is mounted to a lever and is offset in a way that changes the spacing between the pins when the lever is moved. This allows you to very precisely measure how much a bicycle chain has stretched. The stretch amount is visible through a small window.The tool is machined out of solid aluminum and the color is anodized (not painted). There are no plastic or fragile parts. The tool will never wear out -- one is all you'll need for the rest of your bike-riding life.Chains have a sequence of narrow & wide links. Each narrow & wide pair of links on a new chain will measure exactly 1.0" from center of pin to center of pin. If you were to use a ruler to measure 20 links (10 "pairs") it should measure exactly 10.0" on a brand-new chain. The chain will stretch with use as the hinge points wear. 1/16th of an inch is normal -- at 1/8" it's time to replace the chain. But using the Park Tool is a easier and faster than using a ruler.Set the lever to the "0" position and set the tool on your chain (keep mild tension on the chain to get an accurate reading -- measuring a chain hanging slack will not be accurate) so that the pins on the tool are between the links on your chain. Push the lever until it stops then read the stretch value through the window on the tool. A brand new chain will measure .0 -- any used chain will have some stretch. Values below .5 are considered normal/acceptable amounts of wear (the tool reads from 0 to 1.0 in .25 increments.), but above .5 means your chain will need replacing soon. I replace my chains when they read .75.Why do you care?Chains are relatively inexpensive and easy to replace, but if they're not replaced they can create problems. The chain will begin to slip and jump -- usually under heavy load such as trying to ride up a steep hill or on an aggressive climb on a trail (which is exactly when you _don't_ want that to happen). A stretched chain will also wear the sprockets -- it'll mildly affect the front chainrings, but it can more rapidly affect the rear freewheel or cassette and these are more expensive to replace.If you ride aggressively on trails you should be checking your chain about every 100-200 miles of riding. If you ride more gently or only on mostly flat streets then you may only need to check every 300-500 miles.I give this tool 5 stars (and I'm not one to just give out five stars because I bought one myself) because it's simple to use, it's easy to read, it's accurate, and it's constructed of durable materials -- not cheap plastic parts -- down to every detail (including anodizing the aluminum instead of painting it -- so there's not even any paint to wear off.) They did everything right when they made this tool. I couldn't ask for anything more.

Absolutely simple easy and well constructed. Best chain checker tool on the market. Works on single speed and multiple speed bikes. This is a must-have item and it will save you from having to replace your cogs and chain rings from premature wear.