Is this replacement bolt safe to replace YTS A2-70?

[Roberta]

I snapped the seat post collar (I hope that's what it's called) bolt on my Joe Appaloosa while tightening it,  got a replacement from a local LBS but not sure it's safe.  I recall a few months ago someone had something similar, but I don't remember the specifics.

Bolt that snapped is marked YTS A2-70, the bottom broken bolt in the pic.   The new one is unmarked and is the top bolt, assuming the pics don't rotate.  It's a bit more rounder looking. 

Can I use it temporarily or permanently, or just hold out until I get the exact match?   Learning from this group that one bike is never enough :) , I do have an AHH, so I won't be without a bike.

I never thought that I would have enough strength to do this!  Just this morning, I got the saddle height, tilt, setback just right!  That is why I was tightening it.

Thanks, Roberta

[Patrick Moore]

Roberta: I have to laugh, since it seems you suffer from the same hereditary illness that I suffer from: torque-itis. I've broken the same bolt as yours, and many others as well, and most recently broke a brand-new seatpost collar -- when I ordered a replacement, I ordered 2 for future breakage.

Others will correct me if I am wrong, but I think based on just the general evidence of decades of bike wrenching that there's nothing especially strong about seatpost binder bolts, and that any industry-standard hardware store bolt of the same size will easily hold up to the torque needed to keep a seatpost in place, assuming that the seapost, seat tube, and seatpost collar are all to spec.

I have to keep reminding myself that it doesn't take a great deal of torque to make a seatpost stay in place -- again, if the post, tube, and collar all fit as they should.

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Patrick Moore

Alburquerque, Nuevo Mexico, Etats Unis d'Amerique, Orbis Terrarum

[Patrick Moore]

Come to think of it, here's more evidence, at least indirect, that your new bolt should do fine: at one point Rivendell was designing seatpost clamps to take run-of-the-mill hardware store bolts instead of requiring special seatpost bolts; my 2003 custom had this sort of clamp (the 1999 requires the old-fashioned, clamp-specific bolt*).

* 

[aeroperf]

The one marked A2-70 is stainless steel.
https://www.fastenal.com/content/product_specifications/M.SHCS.4762.A2-70.pdf

A regular metric steel socket head cap screw will work, but you risk it rusting if you leave it in for any length of time.
So you can use the other one, but replace it soon.  I’d check Home Depot.  They keep a surprisingly good selection of metric bolts.

[Patrick Moore]

Is rust really a problem for seatpost binder bolts? Not if you don't leave the bike sitting in salt water! Lube the threads, of course, but you'd do that with a stainless steel bolt, too.

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[aeroperf]

Regular water rusts steel, too.  I wash my bike occasionally, and once I find the right seat/position, I don’t move it for a few years.  So moisture has time to act.
I’m not worried about a standard steel bolt rusting to the point of locking in place.  It is more of a looks thing.  There’s a reason they used stainless to begin with.
The clamp-specific bolt you show also looks like it is stainless.

[Patrick Moore]

I've been wrenching on bikes since 1967 (the old man said snippily, as he expectorated into his stained, white beard*), and I've lived in very humid environments (Washington, DC! Karachi, Pakistan! New Delhi, India in the monsoon season!) and I've neglected my full share of bolts, and I have never, ever seen a bolt rusted so that the threads bound. 

It's not a real problem. Your True Value or Ace Hardware store bolt from the bin is going to last you years, if not decades as long as you apply a bit of grease to the threads before installing, as you'd do anyway to keep it from binding.+

* But I'm not as old as Steve Palincsar! And I don't have a beard. And my hair isn't white. And I'm younger than Steve. I was 12 in 1967.

+ I recently had a bolt bind so hard in the boss that I was sure it would not come out; all the more distressing in that this was a fender bolt on the new Chauncey-Matthews-Replacement-For-The-2003-Riv-Custom. Just weeks, not years. But this was because Chauncey, with all his virtues, had neglected to grease the threads. As it was, the gods were favorable and by patient working at it, I got it out without breaking bolt or stripping threads.

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[Roberta]

 “torque-itis“

Too funny!   I’m usually not like this but I tried to tighten it as much as possible just because I know I’m not as strong as the guys.  I’ll take it down a notch.

Thanks also aeroperf!  I get to go to a hardware store—one of my favorite types of stores. (I really should have gotten my major in engineering instead of business. )

[Dave Johnston]

Stainless steel is about the weakest bolt you can get. A rusty grade 8.8 (typical at hardware store) can be stronger than a shiny stainless. Also there are counterfeit bolts coming out of China. (yes its actually a thing) I bet Taiwan bike manufactures aren't all that careful about their bolts. Now having said that I have used stainless from Ace hardware without a problem, maybe you just got a defective or counterfeit bolt? They usually break when you install not when you are riding so you will probably be OK.

If you want strong go with this:

https://www.boltdepot.com/Metric_socket_cap_Zinc_plated_class_12.9_alloy_steel_6mm_x_1.0mm.aspx

Strength charts:

https://www.boltdepot.com/fastener-information/materials-and-grades/bolt-grade-chart.aspx

-Dave J