As to the effectiveness and/or usefulness of a keyed washer in bicycle headset specific applications, I cannot give any opinions. It is helpful when discussing useless features with others to use similar terminology, and that's why I introduced the term, albeit late in the discussion. Keyed washers may just be a remnant of some other application in machining or some such thing (I would certainly expect keyed fittings in some timing cam applications, where orientation is essential), and many reflector brackets that interface with the headset have these keys to keep them oriented properly relative to the steerer. This type of reflector bracket functions essentially as a keyed spacer/washer. That's probably the historical basis for some threaded steerers having keyways. As long as there's a keyway in the steerer in order to accept a possible reflector bracket, one might as well manufacture a keyed washer for this application. They certainly aren't as ugly as the type of reflector brackets to which I referred.

My apology, I thought the headset washer was a lockwasher, when in fact it's a flat washer.

I found this NASA fastener design guide, which explains the gory details of washers on pages 9-10.

It's cool; I wasn't referring to anything you said, just the keyed washers themselves. Keyed applications elsewhere do have merit, i.e. the Woodruff key system used to secure pulleys to shafts. Of course, these are usually a bit more robust than a bicycle HS, which is why they work.

This brings me to my second point: Nowadays we are so weight conscious that these parts are almost always Al, which is one reason why the key shears off so easily. This wasn't always the case; I remember the all-steel Campy headsets that were the industry standard for forever until the Al units started appearing on the market. Then there were the saw-toothed washers, with serrations that locked into the upper race. Still, all of these headsets required 2 wrenches to properly install, and if you tried to use only one wrench the key would jam into the steering tube threads.

The reflector bracket came later as the Consumer Saftey movement gained momentum; don't get me started on them...

I agree that it's certainly not a substitute for proper usage of headset wrenches.

My mistake for calling it a lockwasher to begin with =)
Below is a reply I recieved through email from Sheldon Brown regarding the washer:

"I don't see this as a "safety" issue. I wouldn't worry about the
lack of the keyed washer. As long as the locknut is nice and tight
it should be fine. The main disadvantage is that you need two
wrenches to adjust it.

Even if the headset should loosen up it's not a big deal. When I was
a kid I used to ride a bike where the headset was always loosening
up, and I'd just tighten it by hand. Never caused any handling
problems.

All the best,

Sheldon"

Can anyone tell me how to cut a keyway in a steerer to receive the tab on the lock washer?

Thanks

Don't!!! If your steer tube does not have a keyway, it probably isn't English threaded (maybe it's obsolete French threaded?)

Also, cutting threads or a keyway into a steerer is a very dicey affair. You would need precision machining equipment to do this procedure, and you might weaken the steer tube. You don't want to break your steer tube. That's about the worst failure mode possible for a bicycle. I suggest never making any modification of a steer tube from its factory condition.

French headsets use a flat instead of a keyway. The fact that a steerer doesn't have a keyway is not an indication that it's French. The biggest benefit of both styles is that they hold the hanger for centerpull brakes in the correct position and bumping that bracket doesn't tend to knock the headset out of adjustment.

The shop I bought the forks from suggested filing a flat on the steerer, but that doesn't sound good as I could mess up the threads and I'm not sure you could file enough to accept the key - has anyone done this successfully?

A London bike shop I went into today told me just to file off the key on the lock washer. Sounds like that's the best option to me.......

Sure. There is this thing called a fork cutting/grooving guide:

https://www.biketoolsetc.com/index.cg...m_id=UB-GROOVY

Using this $45 tool will likely screw up your nice threads on the column. Then you will need to buy another expensive tool (a 1" die or thread chaser) to fix the threads.

But, this is a total waste of time and money. You don't need the washer (keyed, or otherwise), or the groove in the fork column. Just adjust the headset loading and tighten the two nuts against each other. NASA references aside, this ain't rocket science.

This thread is a classic example of people wanting to make things WAY more difficult then they really are.

That's exactly what you should do.

Yeah, use a circular file and grind off the tab on the washer itself. That actualy works better becasue a lot of times, when tightening the locknut down, it spins the washer and the washer gets stuck on teh groove. THen it prevents the locknut from pushing down hard enough to lock everything together and the headset ends up loosening.

Another trick is to use two wrenchs and unscrew the adjustable cup up into the locknut which is being tightened down THis really locks them together and prevents loosing under load.

Ding ding ding. Most threaded headset have a locknut.
LOCK NUT: A type of nut that is used to prevent another nut or threaded component from loosening and backing off. The keyed washer isn't necessary if the locknut is used properly.

"Threaded headsets often have keyed washers between the locknut and the adjustable race. The key on the washer is not only unnecessary and likely to damage fork threads, it may even interfere with securing the position of the adjsutable race. The keyed washer tends to rotate and jam it's key into the fork threads. When this happens the washer is no longer capable of transfering the force down to the adjustable race since it is stuck against the fork threads." Barnett's manual volume 1, fifth edition page 11-14