screwdrivertools
I have two different sized Phillips screwdrivers that both say they are 00 sized (click here for full-sized image):
The green screwdriver came from an iPhone 3/4 disassembly kit, and on the package it says "Phillips#00". The tip is about 1.5mm wide.
The screwdriver on the bottom is a Craftsman and it says "P-00" on it. The tip is about 2mm wide.
One of these screwdrivers cannot be 00 sized. Which one is 00, and what size is the other one?
A right-angle screwdriver will probably work for your situation. They're also fairly inexpensive.
As for "bendy" screwdrivers, they do make them under the label "flexible shaft screwdrivers," but most of them have pretty low ratings on Amazon. The best one appears to be the EazyPower Flex Extension, which is meant to be used with a drill.
If you can use a drill with a screwdriver bit to drive a screw, then most of the time, use it.
Here's when you might be smarter to use a screwdriver:
The screw is going into a pre-tapped (threaded) hole in metal, or plastic, or any soft material.
Always at least start such screws by hand -- so that you can avoid cross-threading them.
Putting screws into delicate assemblies: eyeglasses, electronics, medical prosthetics, etc.
When working in cramped spaces, a drill/driver often can't fit. Screwdrivers come in flexible, stubby, right-angle, etc. varieties for such occasions.
For emergencies or odd jobs. Multi-bit screwdriver tools are dirt-cheap now. I have one in all my vehicles. I keep one in my briefcase, one at my grandmother's house, etc. You'd be surprised how often something needs to get screwed ;) and I certainly don't have dozens of cordless drills and chargers.
When the environment is likely to damage an electric device -- working in the rain, or in the mud under a house, or in a very gritty environment, etc. (Note that this is one more reason to make employees buy their own tools.)
When working with a material where finish is important. A driver is much more likely to strip the screw interface, or to slip and mar the material being screwed, or to drive the screw too deep and crack or warp the surface of the material.
When driving slot-head screws. These are notoriously hard to drive with a drill; the bit flies out of the slot too easily.
When a precise torque is needed. (NEVER trust the torque setting on a motorized driver unless it is one of the industrial models made for that purpose and it has been recently calibrated.)
When the screw itself is delicate, such as plastic screws, soft metal screws, threaded wooden dowels, etc.
When working around volatile chemicals or in an explosive environment.
When working in a clean-room environment, screwdrivers are much less likely to contaminate and are easier to sanitize/sterilize.
When chemical or radiological contamination is an issue. A plain screwdriver is much easier to decontaminate.
When the power has failed and/or the battery is dead (batteries also stop taking a charge after a while and need to be replaced). Thanks to ratchet freak for the reminder.
When you want a nice vodka "kick" to your orange juice.
Best Answer
The Phillips screwdriver size is based on the size at the very tip. Based on diagrams of the tip from the original Phillips patent (shown in one of the links to sizes.com), I'm guessing that the relevant physical size is the cross you see when you point the screwdriver at your nose (as though it were a screw) and look at it end-on, or something directly related to that. How much the tip widens to become part of the shaft is irrelevant. You could make one that widens to a meter in diameter, making it nearly impossible for humans to use.
I tried this experiment: using some digital calipers, insert just the tip between the calipers, and measure the distance from one point on the cross to the opposite point. This is difficult to do accurately since if you insert a little more than the tip, you get a result that is too large. I tried several different sets of screwdrivers and bits for them from different manufacturers.
The results: PH3: 0.141 inches, PH2: 0.086 inches, PH1: 0.071 inches, PH0: 0.055 inches, PH00: 0.048 inches, PH000: 0.039 inches, and PH0000 is so tiny I really couldn't get a consistent reading. I don't have a PH4 and I'm not sure I've seen one. As I said, it's difficult to get an accurate reading. I can quite consistently eyeball the difference between a PH3 and a PH2 or a PH2 and a PH1. It's difficult to consistently see that a PH00 is larger than a PH000. I can see that like sizes give similar results, and measuring the same bit over and over also gives similar results, however, the ranges for adjacent sizes overlap a bit for PH000, PH00, and PH0.
A serious attempt to make these measurements would probably require several vices, a powerful magnifying glass or a microscope, and digital calipers with a thinner edge than the set I have. Either that or I'd need about 6 hands.
I presume a PH0000 screwdriver is intended to drive #0000 screws, a PH000 screwdriver is intended to drive #000 screws, and a PH00 screwdriver is intended to drive #00 screws, as these seem to be the only screws smaller than #0 in the inch-based "numbered screw" system. There could be a #00000 screw, but it's less than one-hundredth of an inch wide and probably can't take much torque, and a #000000 screw would have a negative diameter, which is obviously impossible.
Somewhere buried in an ANSI standard is the physical dimension that determines the driver size. I may have found one of them, but it costs $65.