Outside magazine, March 1995
Even if you've got a surgeon's hands and a frame-builder's knowledge of bike anatomy, a chain tool is your only hope of riding out if your chain breaks on the trail. The chain tool is designed to mesh with your chain and then push a connecting pin out just far enough to separate two links -- but not so far that the pin falls out. Later, it'll put everything back together again. Follow the instructions that come with the device, because models vary. Practice moving the pin so that just a bit of it protrudes on the inside of the link when you separate it; then you can reconnect the links by hand, and you won't have to fight with the tension of the rear derailleur as you line up the chain tool to finish the job.
Two more things: If the chain is stiff where you reconnected it, flex the area laterally and work the stubborn link back and forth with your fingers until everything moves freely. If you bust more than two or three links on a chain, get a new one installed. Yours is probably past its prime, and the missing links will certainly shorten the chain enough to impede shifting.