Screwdrivers are a necessity and come in all shapes and sizes and each are equally important, you can never have too many it seems.
Here are some standard shaft lengths and their uses;
Stubby for tight spaces usually have a shaft length of 1-1/2″
Standard for all around good use have a shaft length of around 4″
Tall and skinny for hard to reach spaces (tall and skinny can snap easy if heads are over torqued) have a length around 8-12″
Thick and sturdy ones can come in any length, the width is what is important here. These are good for using as small pry-bars as well as hitting them with hammers to get over-torqued stripped ones out or to knock things in and out of tight spaces.
Head shapes and sizes and their uses are;
Flat head, also known as slotted driver are one of the most basic tools ever designed. They come in a variety of sizes and lengths, with each meant to serve a specific purpose. They often serve as a miniature pry bars, scrapers, or chisels too, beyond their driving capabilities. Each size uses the same basic design with differences lying in the length of the shaft as well as the width and thickness of the driver itself. These tend to strip easy when trying to torque down so they are best used on adjustable settings or even applications just requiring a snug fit, like electronics.
Phillips, also known as cross driver are the more popular screw brand because they tend to torque better and strip less. Like the flat-head, they too come in many shapes and sizes but they are indicated by numbers, not fractions. Head numbers can fit multiple screws, here are some numbers with matching screw numbers;
Head #0 fits #0 and #1 screws.
Head #1 fits #2, #3, and #4 screws.
Head #2 fits #5, #6, #7, #8, and #9 screws.
Head #3 fits #10, #12, #14, and #16 screws.
Head #4 fits #18, #20, and #24 screws.
Of course, you can also learn head to screw sizes by trial and error, pending on torque of the screw needing to be loosened, heads may fit other screws not associated.
Torx, also known as a star driver seem to be more common nowadays as new automobile models come out with more electronics. Initially they were used more as a tamper resistant. Their sizes range in numeric as well but with a “T” defining it, such as T1-T10, then going to T15, T20, T25, T27, T30, etc. These are only a necessity if you plan to work on electronics or know that your vehicle has multiple torx heads.
Nut-drivers are used to tighten nuts and bolts requiring much less torque than a wrench or ratchet is needed. Mainly used for electronics and connectors that just need to be snugged up. They tend to have hallow shafts to accommodate shanks/bolts that nuts are on. There are different variations of these as well;
1/4″ DRIVE HANDLES
1/4″ drive handles for switching sockets but as you can see, these are shallow drivers so if you’re trying to wrap around a long bolt you will need the standard or following types.
T-handles for better handling and hallow shafts
Inter-changeable drivers have hallow shafts with a hallow slotted handle for quick and easy change outs. You can find kits of all drivers in this style.
These multi-drivers are very handy to have. Not quite as strong as standard drivers, these hold their own for standard jobs not requiring too much torque. Some swivel, some ratchet, some even work as storage containers for other bits.