The ShockStop handlebar clamp is 31.8 mm which is compatible with many modern bikes, without the need for shims. However, some bicycles have different size handlebars which may require the use of shims to fit properly into the ShockStop handlebar clamp. We have shims available for 26.0 mm and 25.4 mm handlebar sizes. 

- 25.4 mm is common on bikes with flat handlebars.
- 26.0 mm is common on older road bikes with drop handlebars. - There are other less common sizes that we do not provide shims for. However, other handlebar shim sizes may be available at your local bike shop. 

The easiest way to determine your handlebar size is to see if it's printed on the handlebar. This will require removing your current stem faceplate. 
 

If you can't find the printed size, there are a couple ways you can measure your handlebar: 

Best method: Use a pair of calipers to directly measure the diameter or take your bike to the local bike shop and they will be able to measure it for you. 
 

Alternate method: Use a fabric or paper measuring tape (or print one at https://printable-ruler.net/ ) and measure the circumference of the handlebar right next to your existing stem. 

- A 31.8 mm handlebar will be 99.9 mm in circumference at the center.
- A 26.0 mm handlebar will be 81.7 mm in circumference at the center.
- A 25.4 mm handlebar will be 79.8 mm in circumference at the center.


Keep in mind that 25.4 and 26.0 mm are very close in size. 
 

If you are not able to measure your handlebar, and you know the make, model, and year of your bike, you may be able to find the handlebar size online at your frame manufacturer's website.