Screwdrivers: JIS vs Philips?

depends on the criticality of the fasteners and how long they have been in there.  99% of time, appropriately sized Phillips is fine...but impact is your friend.  BOTH systems are designed to cam out.

Been taking stuff apart with screwdrivers for almost 40 years, never heard about this jargon. Cam out? JIS (I imagine that's Japan Industry Standard?).... Translate fastener geek into English, please?

The link in my post explains it all. But for the TL/DR types that still demand knowledge minus effort.

Cam Out is a driver's tendency to lift out of the screw head when torque is applied. Some Screw Drive heads like Phillips are DESIGNED to do this, it's a Feature, not a bug. Or at least it is until you need to remove one that doesn't want to come out. Then the more Torque you apply the more force INTO the screw along the axis of the driver you need to apply or the driver will cam out and probably start stripping the screw head. One way around this is to use an Impact Driver which you strike with a hammer to both drive the tool into the screw head, and break the screw free about 10 degrees or so. If you work on anything older than say 10 years old, you need at least one if not a big one and a little 1/4" bit version.

JIS: Japanese Industrial Standard B 1012:1985 This screw drive is meant to not cam out and is used in manufacturing where torque limiting tools are used, so no cam out damage to the screw, AND no over torque. It's why every older japanese bike has stripped engine screws because people try and remove them with Phillips drivers and mangle the already soft sometimes aluminum screw heads. If you see a little dot next to the drive slot on a screw that's JIS.

Woe unto all foolhardy mechanics who attempt a Japanese motorcycle carb rebuild without heeding the warning of the tiny divot on the screw head. For their life is a sad and angry one filled with screw extractors and praying to the eBay gods that they can find a replacement carb.

How are those Impacta? I've had my eye on them for a while. I mean when you aren't using them for impact just regular turning?

...and don't forget the corroded clutch/brake reservoir covers that you try to remove only _after_ draining the hydraulic fluid... I had _ass_umed that I knew it all because I knew that Phillips != Pozidrive and how to tell the difference...

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. . . and what sort of black magic are those Impacta screwdrivers?  Every other screwdriver warns you not to pound on them (which we all do anyway to get frustration out before proceeding to the chisel/grinder/oxy-acetylene/napalm) - but these you can wail on with a 5lb sledge and they _work_?

I meant more as regular screw drivers. I've seen them used as impacts by AvE, just wonder if they are a total replacement sort of thing or best left only for impact jobs? How much slop do they have when just used without hitting them?

They are kind of heavy but I use them as regular screwdrivers when i need a bigger phillips head screwdriver (these are my "big ones").

I will admit though that of my motley assortment of tools, my screwdriver drawer is the MOST assorted set of them all. I don't have a cohesive "brand" with all the different sizes lined up in a row along with a few extra orphans. Instead, I have a drawer full of random free HF screw drivers, cheapie screwdrivers, the two Impactas, and some others that in total approximate all the sizes of screws I've ever had to deal with (not including the two jeweler's sets from HF I own). It's not pretty but it works for me (for now). I kind of look at it like Battle Royale: the truly shitty screwdrivers die off quickly so what's left are the ones that were just decent enough to stay useful and keep their place in the drawer.