Bicycle Mechanics - Where to buy left crank arm nut?

I am fixing a friend's old 1970s department store bike (Free Spirit ladies 10-speed). The left crank arm nut that holds the crank arm onto the crank stub is missing, and the arm falls off the square shaft. I believe the left crank arm is reverse threaded, right? I measured the outer diameter of the threads onto which the nut goes, and it measures approximately 10mm. I have looked around online and can't seem to find this nut on any online retailers. The crank is a Sugino, for what that's worth. Any suggestions where I could go to find this nut?

Any LBS near you should have them for about $1 each. Basic crank nuts/bolts are not left/right specific.

take the one off the other side with you, the only left handed threaded bolt on the bike is the left pedal.

Isn't it just one of these?
http://www.amazon.com/ACTION-B-BRACKET-AXLE-SQUARE-TAPER/dp/B001ANS5PS

Isn't it just one of these?
http://www.amazon.com/ACTION-B-BRACKET-AXLE-SQUARE-TAPER/dp/B001ANS5PS

Go to a bike shop, and it will be probably be half that price. Take 'em a beer and it'll probably be free.

BTW. That nut will not fix the problem. You need a new crank arm as well. No really, you do. If the arm fell off, without having to be pulled off with a puller, the square taper press fit is corrupted and the crank will not stay on. You can either accept the advice of someone who has been repairing bikes for 30 years or go make you own mistakes.... :thumb:

^^^ +1

+1 While I buy a lot of stuff on line, some things do not make sense, particularly low $ items where the shipping is likely to be greater than the item's price.

As a side benefit, have the shop look at the crank arm, could have more problems that a replacement nut will not fix.

Agreed. Would you go to Acehardwareonline.com to purchase a 1/4x20 nut and bolt? I don't get the reason for spending time searching for a $1.00 part, particularly when the mechant who sells you the part has no ability to come through your Internet connection and say "That part is not going to be compatible to me," or "I would recommend checking that crank arm for damage."

(Fair warning - Here he goes again)
The people who avoid bike shops strike me as kind of reverse Luddites - the Internet is high tech and therefore better than the old-fashioned bike shop. Well, guess what? You will likely learn far more from a few visits to a bike shop than from hours spent reading questionably qualified posts on this or any other forum. If you only have one bike shop and it "sucks" then look for a local bike club and ask if they offer any repair clinics, or look for a local cyclist who like to help others.

Believe it or not, people learned how to fix bikes before the Internet existed, and even before there were dozens of bike repair books. When the 10 speed boom hit we did not even have many other folks to help us - we had to figure out how things worked by observation. I'm not saying that as a "we had to walk 10 miles to school" rant, because nothing has changed. Observation, backed by information as it is available, is still the best way to understand working on a bicycle.

p.s. If you don't know the threading of a BB spindle, and don't know that a nut will not fix the problem, then you probably should not be working on someone else's bike.