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Condensed Info: There are three main reasons why a bike pedal won’t screw in. First, you’re trying to install the pedal on the wrong side (e.g., the right pedal on the left).

Second, you’re rotating the pedal in the wrong direction.

Third, the pedals or the crank’s threads have been damaged and do not allow a tight connection.

Bike Pedal Threads

The left and right bike pedals have different thread directions. (The left pedal is on the non-drive side; the right pedal is on the drive side).

The left pedal has a left-hand thread. This means that the pedal is installed by rotating it counter-clockwise and can be removed by rotating it clockwise.

Meanwhile, the right pedal has a right-hand thread. To mount it, you have to screw it in clockwise.

The reason for this thread choice is to prevent the pedals from unscrewing during pedaling.

If you’re trying to install the right pedal on the left or vice versa, you won’t be able to mount it without damaging the threads of the cranks.

If you’re rotating the pedal in the wrong direction (e.g., the left pedal clockwise), it won’t screw in either.

FAQ: How can I learn if a pedal is left or right? They look the same to me.

Most pedals have a single-letter indication near the threads. “L” stands for left and “R” stands for right.

If the pedals don’t have an indication on them, look at the threads. The threads of the left pedal tilt to the right whereas those of the right pedal tilt towards the left.

Be Careful Of Cross-threading

The pedal threads are on the pedal axle. The axle is made of very strong steel because it has to support the rider’s weight (when pedaling out of the saddle) as well as the torque generated by the rider’s legs.

Meanwhile, most crank arms are made of aluminum or carbon to save weight and make the pedaling experience better. If the pedal isn’t inserted carefully, or if the user tries to install the wrong pedal, it’s very easy to cross-thread the crank arms. When that happens, the dense steel axle will damage the crank arm’s threads.

Note: To avoid cross-threading do not use a wrench initially. Instead, try to tighten the pedal with your hands first. If everything is fine, you should be able to get a couple of spins without exerting a lot of effort. Then, use a wrench to fully tighten the pedal to the required specifications.

If the crank arm threads are damaged, the user will not be able to securely mount the pedal. One of the common solutions is to re-thread the crank arm and then insert a threaded insert. The process is shown in the video below:

Damaged Pedal Threads

The initial pedal threads are susceptible to damage. If the first few threads are damaged, you won’t be able to screw in the pedals. The solution is to repair the threads by using a 9/16″ x 20 thread die.

Note: Don’t forget that the direction of the threads changes for each pedal. If you’re repairing the left pedal, you will need a left-hand thread die.

The Pedals Could Be The Wrong Size.

The size of most pedals is 9/16″ x 20.

9/16″ x 20 TPI stands for:

9/16″ (14.3mm) is the diameter of the pedal’s threaded part.

TPI is an acronym for Threads Per Inch and shows the number of threads per 1 inch/2.54cm. In this case, the threads’ density is 20 per inch or 20 per 25.4mm which amounts to 1.27mm between threads.

However, there are also 1/2″/12.70mm pedals that have a thinner axle. Those are usually found on the BMX market and are designed for single-piece cranks. If you have a 1/2″ pedal, you won’t be able to mount it to standard cranks.

There are two solutions. A) Replace the axle B) Get a new pedal.

To learn more about this topic, consider reading this article.

Contamination

If the threads of the pedals or the cranks are full of debris, it will be difficult to screw the pedals in. Use a degreaser and a rag to clean the area. That said, this is rarely the source of the problem.

Summary: What You Need To Know

In most cases, the pedals cannot be screwed in because:

1. You’re trying to install the right pedal on the left or vice versa.
2. You’re rotating the pedal in the wrong direction.
3. The threads of the crank arms are damaged and need re-tapping.

It’s also possible to experience this problem when:

1. The initial threads of the pedal are damaged.
2. The pedals are not the right size.
3. The threads of the pedals and the cranks are contaminated.