further to my other thread (about fitting a bar/stem) have been wondering what the star nut actually does.also,when i fitted my stem (flush with the top of the steerer tube).the guy at the shop fitted a washer on top (as he said that i wouldn’t be able to tighten the top bolt?) just wondered why.sorry to be a numpty,but if you don’t ask,you don’t get as my old grampa used to say 😉 thanks 🙂

Doesn’t it hold the headset together, i think.

The SFN enables you to tighten the headset with the bolt in the top. Then you tighten the stem to keep it all in place.

If the stem us flush with the steerer, the top cap tighten on the steerer. It needs to push on the stem to transfer the load to the headset, hence the spacer!

🙂

Pulls the headset assembly together

Threadless headsets are adjusted by pressure on the top bearing race. Pressure is applied when the bolt in the top cap is tightened. The stem bolt(s) must be loosened, which makes the stem effectively a spacer during the adjustment. The bolt is threaded into the star fangled nut which be fitted into the inside of the fork column. The star nut is designed not to pull upward. In other words, it is designed not to be removable. The star-nut outer diameter is slightly bigger than the inside diameter of the fork column. This allows the flanges to bite into the fork walls and hold it tight.

Michael, no it doesn’t actually hold it together, the stem does that. It’s used to gently take the play out of the headset. Once the stem pinch bolts are tightened, you can take the top cap off and it won’t fall apart!

It preloads the bearings – you couldn’t just push the stem onto the steerer by hand and clamp it.

Nuts stars and fangles them. As any fule kno.

It is needed to pre-load the headset bearings.

If you don’t have a gap between the top of the steerer and the top of the stem (or spacers on top) then you can’t pre-load the bearings properly and you will get a horrible sloppy headset which will knacker it’s bearing in no time.

There is no way you could manually push down on the stem enough while tightening the bolts to clamp it up to get rid of the headset play.

Technically you could put a long threaded bar down your steerer and use some nuts to preload the bearings and then tighten the stem and remove the rod leaving just a nice hole down through your steerer. But if you headbutt it you might get your forehead apple cored 😀

The slack in your headset bearings is taken up by compressing them with the stem. This is acheived by pressing down on the stem with the top cap by tightening the bolt into something attached to the fork’s steerer tube, that “something” is the star fangled nut, a device that can be easily fitted to whatever length of steerer tube is required.If your stem is flush with the top of the steerer, then you’ll be unable to pre-load the bearings as the top cap will bottom out on the steerer first.

I nearly posted on your other thread to check that you didn’t tighten the bolt through the top cap too much, thinking that it held it all together.

I assumed that you had some instructions from somewhere as you were change things over.

Zinn and the Art of Mountain Bike Maintenance is a good book for learning about these things.

Get the one that is current when you bought your bike as future editions might not be so relevant.

how many different ways can we say this? I do remember trying to tighten my mates first aheadset without one – not very successful.

One thing it does very well – is to cost far less than the alternatives.

or just bookmark the Park tools site: http://www.parktool.com/blog/repair-help/threadless-headset-service

thanks everyone,i understand now 😀

CFH
Nuts stars and fangles them. As any fule kno.

Its a star fangled nut fule! It stars nuts and then fangles them. Otherwise it would be a nut fangled star, and we all know they are for Xfactor USA only.