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This has been bugging me for a while. I've always had penknives/pocket knives (Swiss Army knives), and even the cheap ones are made of stainless steel. They include screwdrivers and other similar tools to bike multitools. But my bike multitools tend to rust, badly, if they get wet (and they do get wet, as I ride in all weathers in a wet country). The only stainless ones I've got are small and effectively incomplete, though I see that Lezyne make one and possibly Topeak (or maybe that's just the body)

So is there a good (engineering) reason why bike multitools are rarely stainless?

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  • I guess you can think the other way around: would you want to eat something you've cut with an extremely rusty knife ? Then knives have to be stainless. Jun 11 at 9:40
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    @VincentFourmond many kitchen knives are carbon steel - but cared for properly that's not a problem.
    – Chris H
    Jun 11 at 9:55
  • E.g. the Crankbrothers M19 and probably others come with an aluminum&plastic case that is somewhat watertight. Unless submerged, it should keep the tool dry. You could add a plastic bag inside to improve water resistance...
    – Erlkoenig
    Jun 11 at 10:18
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    @Erlkoenig I'm no weight weenie, but a case for a single tool is dead weight and bulk. I uses a reasonably well-sealed tool bottle under the downtube, but that has been known to get immersed, and I seem to have to open my tool case in the rain quite often. Once some rain gets in, it stays there
    – Chris H
    Jun 11 at 10:22
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I believe the reason is hardness for the tool steel. With carbon steel you can achieve harder steel, at the cost of some brittleness, at much lower cost. There are some very hard stainless powder steels but they are also very expensive.

Some CrV steels used for tools have some rust protection due to the chromium content, but are not fully stainless. Also, even stainless steels can and do rust. Especially the harder types.

Note that cheap stainless knives are usually pretty soft and require frequent honing.

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    Victorinox, as far as I know, does not really use particularly hard steel (HRC 53), rather very corrosion resistant ones, and is among the cheaper mass-produced brands. Compare with, also mass-produced, Spyderco.
    – Vladimir F
    Jun 10 at 15:18
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    Note that European even professional chef knives (e.g. Zwilling, Wuesthoff) tend to be softer and more corrosion resistant and they are expected to be honed regularly.
    – Vladimir F
    Jun 10 at 15:26
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    I suppose given how little engagement you get in some bike hex head fasteners, which also use undersize tools compared to other applications, you really don't want the tool rounding off so need greater hardness
    – Chris H
    Jun 10 at 16:18
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    Tools are quite often used with greasy hands and tend to be slightly oily, so that they won't rust too easily. It's different for knives with water, aggressive plant juices etc.
    – Carel
    Jun 10 at 20:13
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    This is largely correct, but in turn begs the question of why many bike multitools don’t have a good passivation layer on their metal parts. Ferritic nitrocarburization is obviously way too expensive for this type of thing, but parkerization is relatively cheap and would measurably improve the useful life of many such tools in particularly wet environments. Jun 11 at 2:23
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Basically, with stainless, it's either soft, or brittle, or both, or ten times more expensive.

There are stainless bike multitools in the usual (unergonomic) format but... meh, one of the comments says "the bit snapped". If you can't trust the tool to fix the bike, then, well... And the bits are not replaceable, so when they snap, ka-chink, buy a new tool.

I've got this tool:

enter image description here

I put it in a plastic bag, yet after a few years the bits got rusty. But on this tool, they are easily replaceable, which might actually solve your problem.

Even if the ratchet rusts and seizes, it'll still be usable (just without the ratchet action).

The chain rivet tool is the best I've used. The tool is very ergonomic and a pleasure to use. In fact I used it more for DIY and screws/bolts in tight places, than on the bike.

If you really like rain, and don't like rusty tools, you could use just a a set of bits and a small "waterproof" chrome plated hex wrench that fits the bits:

enter image description here

There are also swivel head versions available.

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  • That tool does look reasonable, but by the time I'd added the other things I've got on mine I may as well carry a non-bike mini socket set, chain tool, a mini leatherman (I may end up doing something like that when I replace the rusty one)
    – Chris H
    Jun 11 at 20:02

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