RichinSC1

I am installing bar end shifters into my handlebar but the width of the shifter is 1mm larger than the open end of the handle bar. Is there a way to expand the handlebar opening either by brute force or heat?
The width of the shifter is 19mm and the inside diameter of the handle bar at the end is 18mm. Thanks for your reply

HTupolev

No, that's vastly too big of a diameter discrepancy.

That's an unusually narrow bore for a road drop handlebar.

What type of handlebar is this? What is the outside diameter of the handlebar tubing (most likely either 23.8mm or 22.2mm)?

mstateglfr 

Just buy new handlebars with the correct internal sizing needed to fit your bar end shifters.

Curious what brand and model bars you have.

RichinSC1

I have bull horn handlebars and I'm having a hard time finding any new ones that have a larger inside diameter.

HTupolev

What is the outside diameter of the handlebars? Not at the stem clamp, but where you'd grip them.

RichinSC1

21mm OD at the bar end.

HTupolev

That's probably the source of your trouble.

In the industry today, there are two main standards for the handlebar outer diameter. MTB handlebars typically use 22.2mm, road handlebars typically use 23.8mm. There aren't really any firm standards on inner diameter, but 23.8mm "road" handlebar tubing usually has an inner diameter of around 19.5mm or wider. That's what the expanders on bar-end shifters are usually designed to pair with.

If your bullhorns are designed more to MTB spec, then this explains why the inner diameter is too narrow for the bar-end shifters.

This unfortunately puts you in a complicated position. The obvious solution is to look for bullhorns with a 23.8mm outer diameter, as these are pretty likely to play nicely with bar-end shifters. The drawback is that, if you already own brake levers that clamp nicely on your narrow-outer-diameter handlebar, their clamps might not fit properly on a 23.8mm bar, which would be another thing that needs to be sorted out.

Trsnrtr

I've used an adjustable reamer shave a little off the inside. You can buy one at tool stores.

topflightpro

Can you take a file to your shifters to thin them out some?

RichinSC1

Can not file shifter but MAYBE can file ID of handlebar.

Trsnrtr

I've done it a few times. That's why I bought an adjustable reamer.