Nuts and bolts (and washers)

[sjbraun]

I'm woefully ignorant about all things mechanical, but I'm trying to learn. With the help of a friend, I'm learning how to work on my bike.
My current "project" involves setting up my commuter to accept an Ostrich bag from Velo-Orange. This has lead me to wonder about nuts, bolts and washers.
I think I understand why a washer would be placed adjacent to the bolt head,
(to spread the force created by tightening the nut over a larger surface,) but then why isn't a second washer used at the other end, next to the nut?

Steve-whose much better in the kitchen than in the shop

[stackie]

Don't know the answer to your question, but I'll pipe in with a tip. I'd use the leather washers from Velo-Orange if silence is at all a goal. Put them anywhere that your metal rack attaches to the frame.

Jon

[wasfast]

Different washers for different reasons. Flat washers are used to spread the load, usually on the bolt head end but are also used on the threaded end sometimes if the holes are too large. Star/serrated washers can be on the bolt end too. There are also fender or body washers. These have a much larger outside diameter (OD) for a given internal diameter (ID).

On the threaded end you can have star washers, serrated washers, and lock washers. These all are intended to provide additional load to prevent the nut from backing out. Loctite thread compound is used for blind holes. Locktite comes in 3 colors for general use blue, green and red. blue is moderate, green is more and red is near permanent.

On bikes for accessories like fenders, bag mounts etc, use Nylock nuts. These look similar to regular nuts but have a nylon insert on one end. The nylon interferes with the threads, increasing the turn resistance.

This ends today's lesson on washers:-)

[rwsaunders]

http://www.boltscience.com/pages/faq.htm#11

[05Fierte TI]

"locktite comes in 3 colors for general use blue, green and red. blue is moderate, green is more and red is near permanent"

Not quite right. Green is has the least holding power, red has the most, blue is in the middle. To loosen red, normally you have to apply heat to melt the locktite and then loosen the fastener. For a bicycle, I would think that generally green would not be strong enough, blue is likely perfect for most applications and red is too strong as you will need heat and your hand tool to loosen.

That said, I have never used any Locktite on a bicycle. RC helicopters use the stuff all of the time for any metal to metal fastener but never on a bicycle for me.