A wide variety of bike frames unfortunately also means a wide variety of headsets. To help you figure out which upper or lower headset part fits your frame, we’ve broken it down into four quick and easy steps. 

External Cup (EC) 

The bearings are pressed into bearing cups that sit outside the frame. This design is common on older bikes, especially those with steel or aluminum frames. 

Zero Stack (ZS) 

Also called semi-integrated headsets. Here, the bearing sits in a pressed-in cup inside the frame. 

Integrated Standard (IS) 

Fully integrated headsets don’t use bearing cups at all. The bearings are simply placed (or lightly pressed) directly into the frame itself.

Grab your bike frame and measure the internal diameter of the steerer tube at the top. Then note the measurement in millimeters after the two letters from Step 1. For example: EC49, ZS44, or IS42.

Take your bike’s fork and measure the steerer tube at the top. Then write this measurement in millimeters next to the one you noted earlier, separated by a slash. You now have the official designation of your headset upper part, also called the S.H.I.S. code. For example: EC49/28.6, ZS44/28.6, or IS42/28.6.

The fastest way is to use the filter on the left side of our headset page and select the information from the first two steps: 

The headset type (EC, ZS, or IS) 

The internal diameter of your steerer tube at the top in millimeters 

On the product detail page for each headset, you may also have the option to select the correct size for your fork steerer before adding the headset to your cart.