The pedal attaches to a crank arm using a threaded spindle

A bike pedal screws onto the end of your crank arm — the metal lever that sticks out from the center of your bike where the pedals spin. The connection point is a threaded hole at the tip of each crank arm. The pedal itself has a metal shaft called a spindle that screws directly into this hole, similar to how a bolt threads into a nut.

The spindle is the part you don't usually see. It runs through the middle of the pedal platform (the flat part your foot rests on) and extends out to screw into the crank arm. When you pedal, your foot pushes on the platform, the spindle rotates inside the crank arm, and that rotation transfers power to the chain.

The left and right pedals screw on in opposite directions — the right pedal has a normal right-hand thread, while the left pedal has a reverse thread. This prevents the pedals from unscrewing themselves as you ride, since the rotation would otherwise loosen them over time.

Key Takeaways

  • Pedals screw onto threaded holes at the end of your crank arms using a spindle shaft that runs through the pedal platform.
  • The right pedal uses a standard right-hand thread, while the left pedal uses a reverse thread to prevent both from loosening during riding.
  • Pedals can be removed and replaced by unscrewing the spindle counterclockwise on the right side and clockwise on the left side.
  • Different pedal types (flat, clipless, platform) all connect the same way — the attachment method is universal across bike styles.

What the spindle does inside the crank arm

Once the spindle screws into the crank arm, it sits inside a hollow section called the bottom bracket. The bottom bracket is the rotating assembly at the center of your bike frame where both crank arms connect. The spindle passes through this assembly and connects to the opposite crank arm on the other side.

The spindle itself doesn't rotate — it stays still while the crank arms and pedals spin around it. Bearings inside the bottom bracket allow the crank arms to rotate smoothly on the spindle. When you push one pedal down, the crank arm rotates, which rotates the chainring (the large gear attached to the right crank arm), which moves the chain, which turns the rear wheel.

How to remove and reinstall a pedal

To remove a pedal, you need a pedal wrench or a regular wrench that fits the flat sides of the spindle. Position the wrench on the spindle (not on the pedal platform itself) and turn counterclockwise on the right side. On the left side, turn clockwise — remember, the left pedal threads the opposite direction.

Once the spindle unscrews, the entire pedal comes off. To reinstall, line up the spindle with the threaded hole in the crank arm and turn clockwise on the right side, counterclockwise on the left side. Hand-tighten first, then use the wrench to snug it down — you want it firm enough that it won't loosen, but not so tight that you strip the threads.

If a pedal spins but won't tighten, the threads in the crank arm may be damaged. This is a common problem on older bikes or after a crash. A bike shop can repair this by installing a threaded insert or replacing the crank arm entirely.

Different pedal types use the same connection

Flat pedals, clipless pedals, and platform pedals all connect to the crank arm the same way — through a spindle that screws into a threaded hole. The difference is what's attached to the spindle. A flat pedal has a straightforward platform. A clipless pedal has a cleat mechanism underneath. A platform pedal has a larger, wider surface.

The spindle length varies depending on the pedal type. Clipless pedals often have shorter spindles because they're designed for road bikes with narrower frames. Platform and flat pedals may have longer spindles to accommodate wider pedal platforms. But the threaded connection to the crank arm is identical.

Why pedals loosen and how to prevent it

Pedals can loosen over time because of vibration and the constant rotational force from pedaling. Even though the left pedal has a reverse thread to help prevent this, both pedals can still work loose if they weren't tightened properly during installation or if the threads are worn.

Check your pedals every few months by trying to tighten them with a wrench. If they're loose, tighten them firmly. If a pedal keeps loosening no matter how tight you make it, the threads are probably stripped and need professional repair. A bike shop can tell you whether the crank arm can be fixed or needs replacement.

Pedal spindle sizes and compatibility

Pedal spindles come in different diameters, and the crank arm holes are drilled to match. The most common size is 9/16 inch, which fits most adult bikes. Some older bikes or children's bikes use 1/2 inch spindles. BMX bikes sometimes use different sizes as well.

If you buy a replacement pedal, check that the spindle size matches your crank arm. A spindle that's too large won't fit into the hole. A spindle that's too small will spin loosely and won't tighten properly. Your current pedals will tell you the right size — you can also measure the hole diameter with calipers or ask a bike shop to identify it.

Frequently Asked Questions

Can I use pedals from one bike on another bike?

Only if the spindle size matches. Most adult bikes use 9/16 inch spindles, so pedals are often interchangeable between them. Children's bikes and some specialty bikes use different sizes. Check the spindle diameter of both your pedals and crank arms before swapping them.

What happens if I tighten a pedal too much?

Over-tightening can strip the threads in the crank arm, making it impossible to tighten the pedal securely. Tighten until the pedal is snug and doesn't move, then stop. You don't need to use maximum force — hand-tight plus a quarter turn with a wrench is usually sufficient.

Why does my pedal creak even though it's tight?

Creaking usually comes from the spindle moving slightly inside the crank arm, or from the pedal platform flexing. Try tightening the pedal again. If it still creaks, the threads may be slightly damaged or the spindle may be bent. A bike shop can inspect it and determine whether the pedal or crank arm needs replacement.

Can I replace just one pedal?

Yes. Pedals wear out individually depending on how much you use each side. You can buy a single replacement pedal as long as the spindle size matches your crank arm. You don't need to replace both pedals at the same time.