I'm making a crank shortener for an exercise bike that I bought mainly for my father. The ones sold are expensive, over-built for his needs, and wouldn't fit right anyway (the bike has a crank with a round cross section). For the left pedal, I need a 1/2" nut with fine, left hand (reverse) threads. I just need one of these nuts. Five of these nuts on Amazon are over $10 plus shipping. Would bike stores sell such a nut? One of the best hardware stores for this type thing is not too far but their online catalog doesn't list it. Grainger doesn't have it either.

how about this?

and more to choose

When I ran a bike shop many years ago, I used to keep 1/2-20 LH nuts in stock...however that was back in the day when we had an item called 'Repair Pedals' that had an extra long threaded section that protruded through the crank arm and was nutted on the back side. I don't know if they make such a thing these days. Both McMaster-Carr and Fastenal carry that size nut--if you happen to have a store locally...otherwise the shipping will kill you. Most bigger cities also have hardware stores that cater to the commercial trade that may carry such an item.

Look up "fasteners" in your local yellow pages and see if you can find a shop that specializes in industrial fasteners. My little town has a couple of sources for stuff like that.

On the other hand, you've already found a place where you can solve your problem for $10. Any more time spent trying to save $9 might not be worth it! 8-)

My local Fastenal is just outside of my "worth the trip" zone. I think Amazon is my best bet. Then I'll have four extra nuts for...Well, I'll just have them.

Just find a shorter crank off an old kids bike.
I assume you have an Ashtabula crank?

One-piece ("Ashtabula") Cranks

Yeah, I guess. And the red shows my design for the crank shortener.

Are you needing a nut or a bolt?

1/2-20 I think is NFT, so that should be possible to find at hardware stores, except left hand is less common.

You could also buy/use taps, but that won't necessarily be cheap either.

My local Fastenal only sells in "bag" quantities. I suppose those places like to cater to industrial clients, but since I was told I couldn't buy the number of bolts I needed, I haven't been back in there.

Here in Springfield we have a local bolt store that I'll go to from time to time. I just explain what I want and the owner goes back and rummages around until she finds what I need.

Perhaps my $1 to $5 purchases don't really support the store, but lots of small purchases add up over time.

I often get frustrated shopping locally, and often end up ordering online. But, it never hurts to call ahead if you have some particularly odd part that you need.

If you use loctite, or a locknut, then you may get away with building the bike with 2 right pedals, and no left pedal.

Just the nut. I already ordered 5 right hand nuts. If my right shortener works out, then I'll order a left hand nut somewhere.

In my diagram where it says "bolt in old pedal location" I may just use any bolt that could be pushed through snugly and put a nut on it. I'm not sure.

It might be a little awkward, but you might be able to cut the end off of a left crank arm from a kid's crankset. Someone must have a few lying around that they'd donate for free.

Drive around the neighborhood on garbage day looking for good bikes next to garbage cans? Cragslist Free section?

Does this design have the same precession issues as a normal crank? Can you just get two pairs of pedals and just use the RH threaded pedal?

Maybe. If I do that instead of making a crank shortener then the bike would basically be for my father only and I wouldn't be able to switch back and forth.

I meant making a nut out of a chunk of old crank arm. A little grinding, and you could make a good facsimile of a nut. Or at least something you could grab with vice grips.

But, it is a good point, you could also just use a shorter crankset.

Yes, I guess I'd just have to retighten the left one more often, but it wouldn't be worth buying them. I could also use any old single pedal and let them be mismatched. I'm not sure I want to do that.

I live in an apartment and don't have a grinder. I have a hack saw, electric jigsaw, and a file though. Maybe I'll do that if I see a bike left out with the trash.

Note to self: check garbage Sunday after 4:00PM

True Value Hardware and ACE Hardware stores by me have individual nuts.

Unless you happen to find 2 pairs of off-the-shelf pedals cheaper than a single specialty nut.