A2-70 SS Bolts in Flat Mount?

[skom25]

Hi,

Is it ok, to use A2-70 Stainless Steel bolts in Flat Mount calipers?

I used them in PM calipers without issues, but it were M6 bolts. Flat Mount uses quite short M5 and I am little worried.

I see that e.g SRAM has Stainless Steel bolts, but I am not sure if they are better/ worse than mentioned A2-70.

[mathemagician]

Why would it not be ok? FWIW I use A2 torx bolts on my calipers as it's what I had lying around at the time.

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[skom25]

Thanks. I asked because I read many times, that SS is not strong enough for things like that.

[joejack951]

A2-70 is roughly equivalent to metric grade 8.8. -80 is the true equivalent (typically A4 SS, 316) but quite rare to see. Unless you are replacing an alloy steel fastener (like a crank bolt) or a specialized stem bolt, it will be strong enough.

[skom25]

Problem is, that all sources I found says that for A2-70 max torque is ~5Nm. Caliper should be installed with 6-8Nm torque according to Orbea and Shimano.

[Maddie]

If you have doubts about A2-70 bolts, what keeps you from Sram or Shimano bolts?

[skom25]

I do not like TX25 in SRAM. Shimano availability is very low.

Of course I will use them or just stay with TRP, but I wanted to have alternative solution.

[joejack951]

Based on that torque spec, Shimano and Orbea are assuming/insisting that an alloy steel fastener (metric grade 10) is used. That's surprising to me, but you are right to be concerned about using a lower strength fastener. You could try to find some A4-80 fasteners that get you closer to grade 10 strength, or go all in and use A286 stainless steel screws, assuming you can find them in the size you need. All the strength of grade 10, in stainless, but you'll pay dearly for them (>$5 per screw).

Of course, if you simply want an alternative to Shimano/SRAM/TRP hardware, any grade 10 steel fastener will do. You'll likely be stuck with an 3mm hex recess, though.