Bike pedal threads are a tricky thing to get your head around at first, there are a number of different types, and the left and right pedals have different pedal threads as well.
This makes it all too easy to damage the thread on either the pedal or the crank, which can be a very costly mistake. Thankfully this article covers all you need to know about bike pedals and thread sizes, and its really simple once you know!
Types of Bike Pedal Thread Sizes
It would be far to easy if all pedals were the same size and require the same tools to replace. However, this is not the case, but fortunately, there are only two common types that are still produced today.
9/16” x 20 tpi (14.28 x 1.27 mm)
The 9/16” is the most common pedal thread size on the market today and is the size that most manufacturers use for their pedals. Almost all modern adult bikes have the 9/16” pedal with 20 threads per inch (tpi).
This thread size is what you will find on all the big brand mountain bikes and road bikes such as, Trek, Specialized, Giant, and any other big brand out there.
½” x 20 tpi (12.7 x 1.27 mm)
This pedal size is much less common than the 9/16” pedals, but bikes are still produced with these sized pedals today.
Typically bikes with these sized pedals are kids bikes, BMX bikes, and cheaper adult cruiser style bikes. If you have one of these kinds of bikes, then it is likely that you have a ½” pedal thread size.
0.55” x 20.32 tpi (14 x 1.25 mm)
This sized pedal is hardly ever seen these days and manufacturers haven’t used this pedal for quite some time.
The size actually originates from the old-style French bikes as the French back then chose to have their own pedal size.
Thankfully when bikes started to get imported and exported, they stopped making bike pedals with this size and switched to the two that are used today.
If you have a very old French bike, then it is more than likely that this will be the pedal thread size that you have.
One key way to tell is usually the pedals are labelled with a G and a D which interestingly stands for gauche and droite, which means left and right in French.
How to Measure Bike Thread Pedal Size
Fear not, there are a number of ways that you can tell what size pedals you have/require. It requires very little knowledge and will only take a few seconds.
Check the Cranks on the Bike
Manufacturers have made it nice and easy for this one, and all you have to do is check the cranks on the bike.
If your cranks are made up of three separate sections, two separate crank arms and the spindle that goes through the frame then your pedals will be size 9/16” x 20 tpi. Your crank will look something like what is pictured below.
Three Piece Bike Crank
If however, your bike is made of only one piece of metal that is all connected and goes through the bike as one piece, then your pedal size will be ½” x 20 tpi.
This is the easiest way to tell which pedal size you have and is a great little trick.
Measure the Current Pedals Thread Size
If you still aren’t sure what pedal size you have you can also measure the thread width. Since the sizes are very similar it is best to use a set of callipers if you have them as this will make sure you measure it accurately.
It is possible to measure them with a standard ruler but definitely not as easy to tell.
Take it to your Local Bike Shop
If you are still not sure that you know exactly what pedal size you have you can always take your bike or pedal to your local bike shop.
They will be happy to help you out and to find a new set of pedals if you need them.
Bike Pedal Thread Adaptors
If you have bought pedals that don’t fit your bike or there are a set of pedals that you want but don’t come in the size that you need, then there are handy adapters that you can use to solve this.
Types of Pedal Thread Adapters
The adaptors are available for both converting from a ½” to 9/16” pedal thread and vice versa.
This pedal thread adapter is for converting a crank with a thread size of 1/2" to 9/16" pedal thread. This is for using a 9/16" pedal on a crank with a thread size of 1/2".
This adapter converts cranks with a thread size of 9/16" to a thread size of 1/2". It is made to fit pedals with a thread size of 1/2".
How to Install Pedal Thread Adapters
Installing the pedal thread adapters is super easy and only takes a couple of minutes.
First make sure you get the left and the right adapter correct and then simply install the pedal adapter as you would for a normal pedal. Apply a firm amount of pressure to tighten the adapter in place.
Next install your pedal into the thread that is cut out in the adapter. Again apply a firm amount of pressure to tighten and you’re good to go.
It is worth noting that your pedal will sit slightly further out from the crank than normal. This is just because this is where the thread for the pedal needs top sit.
How Bike Pedal Threads Work
Interestingly the way in which bike pedal threads work today was actually developed by the Wright brothers. Yes they built bikes before they created the airplane.
It was their invention that is why the left bike pedal has a reverse thread and the right side has a normal thread. The Wright brothers developed this kind of thread as it means with the motion of pedaling the pedals will actually move in the direction of tightening rather than loosening.
This is great as it stops the pedal from coming loose overtime while your pedaling which would definitely not be fun. If your pedals do come loose then check out our guide on how to fix a stripped bike pedal.
How to tell Bike Pedal Thread Direction
Thankfully on most pedals this is super easy as they have an L and an R written on them. The left hand pedal goes on the non drivetrain side of the bike and the right hand pedal goes on the drivetrain side.
Now if your pedals don’t have an L and an R you are not completely out of luck. You can actually tell which is which by looking at the threads on the pedal.
When you hold the pedal up and look at the thread, the left pedal thread will slope upwards and to the left, whereas the right pedal thread will slope upwards and to the right. Check out the images below which demonstrates this.
Left Bike Pedal Thread Direction
Right Bike Pedal Thread Direction
Well there you have it, thats all about bike pedal threads and the different sizes. Now you won’t need to strip a thread on a pedal or crank again!
If you have a spare set of pedals with the wrong size thread for the crank, then I think that the pedal adapters are a great option to avoid buying new pedals.
Always be careful when threading pedals and never force them in. Its always best to check you are doing it right before making the dreaded mistake of stripping the threads. Check out how to install bike pedals correctly here.