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Shimano uses a screw type that is a mixture between slot and Philips (PH):

Photo of such a screw on a Shimano derailleur

There's a "PlusMinus" screw type for electrician equipment like manufactured by Wiha :

Wiha product image (source: wiha.com)

(Source: Wiha)

Are the Shimano screws officially PlusMinus types? Are they officially Philips (PH) compatible?

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    I would guess the type is actually some sort of JIS (Japanese industry standard) screws, and as so is compatible with JIS screwdrivers.
    – Grigory Rechistov
    Dec 19, 2017 at 20:02
  • Every bolt except the limit screws on my bike uses a hex bolt. Why can't they just fix the limit screws to use hex bolts?
    – Kibbee
    Dec 19, 2017 at 20:35
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    They're theoretically designed so that one can use either a Philips or a regular flat screwdriver to operate them. There is generally no need for a special driver (though I'll admit that such a driver would be handy when the screw is already a bit mangled).
    – Daniel R Hicks
    Dec 19, 2017 at 22:38
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    The lower one, with a diagonal X, is actually a Pozidriv, which has slightly different geometry than a Philips.
    – Argenti Apparatus
    Dec 20, 2017 at 0:53
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    @ChrisH I guess it depends on the type of bike you have, but I imagine that it could be the same size as the left/right tension adjustment bolts for v-brake/cantilever brake arms. This size is quite common and found on most bicycle multi-tools.
    – Kibbee
    Dec 27, 2017 at 13:40

3 Answers 3

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As far as I know, every cross-type Shimano screw is JIS, or at least they are in the sense of being designed to mate correctly with a JIS screwdriver. The limit screws you mentioned just are extended a bit to handle a flat screwdriver if that's what's handy.

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The point of these screws is that you don't need a specific driver. It's just a combination head that will accept either a flat or cross-type driver. Given that your actual screws are worn, you can't really tell what sort of drivers they were designed for. However, at the sort of torques you need to adjust a derailleur, the difference between Phillips and Pozidriv shouldn't be significant, so any of flat, Phillips of Pozidriv should work just fine.

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It is simply a dual drive screw. Use flathead or phillips drivers(probably a size #2). They don't support much torque either way, if you use the screw frequently then replace it with a proper drive like roberston, torx, maybe $0.15 $1 for stainless steel. If you work in a shop just buy a small box of each size in the better drive style.
For a while in the late 90s and 2000s east Asian manufacturers seemed to occasionally mix in those weird posi-drive screws as they kind of look like phillips but I think that has become less common. (personally I would like to see Robertson square drives replace all Phillips, I hate Phillips its one of those antiquated standards used only because it was popular long ago and everybody has one. Phillips is actually designed to cam out as it predates power-driver clutches.)

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    Robertson barely exists outside Canada, so it's not going to replace anything any time soon. And I don't really understand why you're calling Pozidriv (note spelling) "weird" when the whole point of it is to deal with the objection you raise to Phillips. (And, by the way, the idea that Phillips is designed to cam out at low torque is basically an urban legend.) Basically, your entire second paragraph is an irrelevant rant.
    – David Richerby
    Jul 5, 2018 at 17:29
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    They're not Phillips.
    – Nathan Knutson
    Jul 5, 2018 at 18:12

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