Wrong nuts?
 

I ordered these pedals and nuts that would allow me to use the pedals with the crank shortener I made, but I think the nuts don't fit. I just tried putting them on my hand and I couldn't screw even half of each nut on. The description of each pedal says "The thread of the pedal is 9/16" - check your bike or trike for compatibility/fit." What do you think? Do they make a nut for this? What exactly is the thread specification for 9/16" pedals?

9/16" x 20 TPI.. how far off are they (other than 18 being a bit coarser than 20.. with a Pedal tap set You could CHASE the threads ..

Cutting just a Little bit of difference ... is re threading 18tpi out to 20tpi going to work? IDK.

You ever used a Tap and Die set? You Need Oil . there is Cutting oil made for machinists and mechanics ..



Buying a conversion BB and then putting in a shorter arm square taper crank would have been more straight forward an approach, IMO.

In short Wrong Nuts ? Yes wrong pitch..

:innocent:

Is it possible the pedals could have course threads? I just assumed they all have fine threads because my cheap exercise bike with a one piece crank has fine threads.

20 threads per inch is a numerical measurement, of thread pitch frequency and is the standard
that manufacturers of pedals and crank arms try to match, some minor QC variations exist.


Course is Not a Measurement , but a category, in machines some places there is a course and fine thread ,

like Swedish cars in the 60's using some German Parts , the wrench hex may be the same but the Bolts are different.

The 1/2" pedals also used a 20 Tpi standard pitch

France tried to be unique for a while ..14mmx1.25 TPmm, but fell back with the rest , for having an export market.



'/,

The bicycle industry takes from many sources the dimensional "standards" which we bike people deal with. These sources can be metric, ISO, fractional, Whitworth and others, sometimes within the same thread spec (like 10mm axles with 26TPI pitch). This is nothing new and one of the driving reasons Sutherlands started the wonderful manual decades ago.


To the OP's situation. The nuts look to be 9/16x18tpi. Most adult pedals and crank arms use 9/16x20tpi. Given the stress that pedal attachments see and the potential failures (and personal damage) that can (and do) result from pedals falling off cranks I STRONGLY do not suggest any attempt to chase/re tap these nuts. As it is the likely few actual threads of overlap is in it's self a concern, count how many threads are in action with a properly threaded in pedal. Think about the damage to how many threads before the pitches match back up. (close to a half inch by my rough math, which is close to how far a pedal threads into an arm). Then think how the through hole in the adaptor won't support the pedal axle, there not being anything but a clearance fit. So even more stability/support/securement is depending on the nut's ability to tighten down to a large enough degree.


When I read of this project a while ago I just shook my head. Now that I see the lack of homework/understanding about the simple factors at play, thread pitch, I am more worried. Andy.

I successfully made the crank shortener (for an exercise bike) and saved at least $100. Here it is in use:

https://media.giphy.com/media/SCuHSkNyUsYXC/giphy.gif

Then I saw that I needed special pedals that came in 9/16" so I consulted this chart to help my search for a fine thread 9/16" nut. Based on that, I thought I needed to look for 18 TPI. Turns out it's not fine enough, so I need different nuts or any of four or five work-arounds. I may order these and their left hand thread equivalents, or I can get a used crank arm on Craigslist for $10 and cut off the threads to use as nuts, or get a 1/2" to 9/16" adapter (I already have nuts for 1/2" pedals as seen in the video). I can also tap my own. There's nothing to worry about.

I was Just justifying the thread on a soft steel T nut to use a Metric Stainless Bolt in it.

I ordered these pedal extenders. I'll saw them in half and use the female sections as nuts.

I took my 1/2" pedals apart last night and I was thinking of using a cut bolt and coupling nut to extend the axial so it fits the 9/16" pedals but I changed my mind. I'm not sure a coupling nut would fit in the pedal and I can't get metric coupling nuts locally.