How to Expand a Quill Stem to Fit the Handlebars

Expand a Quill Stem Clamp
How to Expand a Quill Stem Clamp

Fitting a handle bar in a quill stem can create scratches on the surface of the handle bar is the clamp hole is too tight, particularly on the top thicker section of the handle bars which often have brand & model markings which are important to preserve to enhance the aesthetic of the bicycle.

This trick can be used for quill stems that have an enclosed threaded section for the clamp bolt as illustrated in the diagram below.

Quill Stem Clamp Expander Trick
Using a nut and bolt to expand the stem clamp hole.

Expander Bolt & Nut Specification

Quill Stem Clamp Expander Bolt & Nut
Sample Bolt & Nut

I found the bolt and nut shown above to expand the opening of my 3ttt quill stem. The bolt must be smaller in diameter than the bolt supplied with the stem and must also be longer so the head of the bolt protrudes when fully inserted into the stem as shown. The nut must be thin enough to slot into the gap as shown. The bolt I used has the following specifications;

Bolt length: 38mm
Bolt Diameter: 4.56mm
Nut Thickness: 2.3mm


  • Use your fingers to make sure the nut does not rotate.
  • Screw the bolt down into the stem. The bolt will eventually bottom out in the stem.
  • Continue slowly screwing the bolt further into the stem. The clamp opening for the handlebars will now begin to expand.
  • Open the hole 1 to 2mm and test if the stem can be fitted onto the handlebars without scratching the wider top section of the handlebars. You may need to widen the hole a little more if it doesn’t.
  • Once the stem is in position on the handle bars, simply unscrew the bolt and remove the nut.
  • Now you can screw in the original stem bolt to clamp the bars in position.


Whilst I enjoy working on my own bikes, I am not a qualified bicycle mechanic. The content of this article is purely illustrative and does not constitute professional advice. For your own safety, this type of work should only be undertaken by a qualified bicycle mechanic. Incorrect assembly of parts could result in equipment damage, personal injury or death.

About Me.

I have been riding and working on my own bikes for many years now. I wanted to share my experiences, knowledge and research with others. My aim is to inspire people to get involved in all aspects of this amazing sport. Cheers.


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