Chains are the heart of your bikes drive train. While levers and derailleur’s get all the glory, chains have the most moving parts, and take the greatest abuse during their lifetime.  They have to be assembled properly to be reliable, and if ridden too long, can cause poor shifting performance and result in additional costly replacement of chain rings and cassettes.   For all of these reasons, I have both a Park CC-3 Chain Wear Indicator and Park CT-3 Chain Tool in my home bicycle tool chest.
Park Took CC-3 Chain CheckerThe Park CC-3 Chain Wear Indicator does one thing; tells you the how much the chain has stretched.  It measures stretch as a percentage of chain length.  You fit one end of the two-sided tool over a roller of the chain, and swing the other end down onto the chain.  If the tab fits into a space between rollers, the chain is stretched the amount indicated, either .75% or 1%.  While a chain with  .75% stretch chain can still be used, a chain with 1% stretch should be replaced.  The stretched chain will result in excessive wear of the cassette, requiring a more costly replacement.
The Park CT-3 Chain Tool is solid and shop quality.  It has both a full size grip and T-bar handle, and shelves for dealing with tight links.  I especially like it for working with my tandem timing chains (where 2 chains must be used to assemble the extra long chain) and my older 6-7-8 speed bike chains.  And while many modern 9, 10, & 11 speed chains come with master links or special pins, the CT-3 will allow you to safely remove links to adjust the chain length. (Always follow the manufacturers instructions specific to the chain you purchase.)
One thing not to use a chain tool for is removing a chain for cleaning.  A chain can be well cleaned on the bike in almost every case.  We will cover chain cleaning in a future post.
If you have additional questions about your chains, or would like it checked for possible replacement, the mechanics at either Bicycle Garage Indy location are ready to help.  And for the do-it-yourself bike mechanic, a wide selection of Park Tools and other bicycle tools Indianapolis are also available.