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View Full Version : The Screw/Bolt Type Guide



Shep
11-05-2016, 07:32 AM
Saw a relevant thread, been wanting to do a write-up for a while now. Wikipedia lists quite a few (https://en.wikipedia.org/wiki/List_of_screw_drives), so I'll use their pictures. Hopefully they don't mind me hotlinking!

Summary Best in Class
Tiny - Torx, Slot, Phillips
Small - Torx, Slot, Phillips
Medium - Pozidriv, Hex, Slot
Large - Hex. Literally just Hex.


Phillips
https://upload.wikimedia.org/wikipedia/commons/thumb/3/3f/Screw_Head_-_Phillips.svg/60px-Screw_Head_-_Phillips.svg.png
Designed to "cam out" and damage the driver rather than the screw. Frequently has problems in practical use, not good for anything that requires torque. Best application is cheap chinese toys or other devices where a screw is designed to hold together rather than secure. Never use for screws that must be repeatedly adjusted, they will damage fast, regardless of how well built. It's an old design that was "good enough" at the time, but in today's world has proven to be a horrible choice for most automotive use cases.

PROS: Cheap, easy to source, come in a wide variety of shapes and sizes.

CONS: Damage is frequent and almost impossible to avoid. Best to keep spares handy for when you need them. Cannot torque properly.


Slot
https://upload.wikimedia.org/wikipedia/commons/thumb/f/f3/Screw_Head_-_Slotted.svg/60px-Screw_Head_-_Slotted.svg.png
Often far better than Phillips head as long as it remains accessible. With a large enough size and proper material of the screw, often has a high tolerance of damage before it becomes unusable. Mixtures of this and Phillips head exist, usually designed as a "back up" for when the phillips gets too damaged and must be removed one final time. Usability is a niche, incredibly small screws use this often purely to simplify the driver and the screw and allow for a decent amount of torque (think: eyeglasses). Larger screws are usually other drive types due to being a better fit. Best used when in incredibly small size

PROS: Usually impervious in larger sizes, excellent choice for tiny screws. Often used in rotary dials to serve as a position indicator.

CONS: Only two possible angles severely limits usability. Better choices available in medium and larger sizes. Useful in a pinch or in a spot that is easily accessible and aesthetically pleasing. Not much use beyond that.


Pozidriv
https://upload.wikimedia.org/wikipedia/commons/thumb/f/f9/Screw_Head_-_Pozidrive.svg/60px-Screw_Head_-_Pozidrive.svg.png
Phillip's arch rival. Looks damn near identical (keep an eye out for diagonal lines), and using the wrong driver can cause damage. Here's a comparison (https://commons.wikimedia.org/wiki/Category:Pozidriv#/media/File:Poziphillipscompr.jpg), "PH" being Phillips, and "PZ" being Pozidriv. Very close in nature, except Pozidriv is designed to not cam out in situations where the Phillips is designed to cam out. This means less damage to both driver and screw, and also allows higher torque. Excellent for situations where "hand-tight" is a good specification.

PROS: Medium sizes are an excellent use case if accessibility permits.

CONS: Small and large sizes are hard to find, likely due to better choices being available.


Robertson/Square
https://upload.wikimedia.org/wikipedia/commons/thumb/5/54/Screw_Head_-_Robertson.svg/60px-Screw_Head_-_Robertson.svg.png
Often good for small-to-medium sizes where aesthetics matter. Over-torque and damage to the screw can be catastrophic, and will often become circles when damaged, requiring screw extraction tools. Never rely on this for torque applications, or anywhere that a drill is unwanted. Bits are often built with low torque in mind, and will round out frequently, requiring a new driver. Great for "install and forget" situations.

PROS: Looks good, can handle better than Phillips on some occasions. Sometimes bundled with Phillips ("Deck Mate") to further avoid Phillip's cam-outs, a special bit is given for that which handles fairly well.

CONS: Does not handle damage well. One wrong move and it's drill time.


Hex
https://upload.wikimedia.org/wikipedia/commons/thumb/b/ba/Screw_Head_-_Hex_External.svg/60px-Screw_Head_-_Hex_External.svg.png
Your standard, everyday bolt. Excellent in medium to large sizes, has the benefit of two drive types: vertical (socket) and horizontal (wrench). Always a favorite for this reason. Complaints often arise when they are too tight, frequently because improper tools are used to remove (12-point sockets, ratchet wrenches, 2-sided wrenches, etc.). When in doubt, use a properly sized six-side socket to remove. Come in a variety of shapes and sizes, however cannot be used in recessed installs without sufficient room surrounding bolt for socket. Still a great choice overall. Don't skimp on the material choice, go with a corrosion-proof material whenever possible.

PROS: Jack of all trades, sometimes bundled with a slot drive on smaller screws, allowing for recessed installs.

CONS: Due to its impervious nature, heavily damaged bolts are still functional. Great when replaced early, failures could mean a snapped head and a ton of work to remove/repair. No "one size fits all" driver, every size has its own need. Still the best choice for most use cases.


Hex Socket (Allen)
https://upload.wikimedia.org/wikipedia/commons/thumb/c/ce/Screw_Head_-_Hex_Socket.svg/60px-Screw_Head_-_Hex_Socket.svg.png[img]
Hex's inverted cousin. Very similar to the Robertson/Square drive above, most of the notes there apply here too. Found in abundance, but cannot be torqued as much as Robertson/Square. "Hand Tight" is often too tight, even if slightly. Larger sizes may avoid this issue with the proper material, but are hard to source. Overall a bad choice, unless that is your goal (end products designed to not be "user serviceable", for example).

PROS: Looks halfway decent, often used for amplifiers due to the "tight" fit the allen wrench allows for.

CONS: Does not handle damage well. One wrong move and it's drill time. Moreso than Robertson/Square.


Torx
[img]https://upload.wikimedia.org/wikipedia/commons/thumb/a/a9/Screw_Head_-_Torx.svg/60px-Screw_Head_-_Torx.svg.png
Small sizes handle very well in terms of torque, these don't strip often in those use cases. Can be made very small and still work great. Allows for precise handling without fear of slippage causing damage to surrounding area, unlike Phillips or Slot. Great for locations where the area immediately around the screw/bolt is fragile or easily damaged (think: circuitboards). Not much use in the automotive realm outside of its electrical circuits.

PROS: Great for installs in close proximity to damageable components, torques fairly well in small and tiny sizes.

CONS: Better choices available for medium and large sizes. Careful when choosing as a "secure" bit: being the go-to drive type for "secure" installations means most thieving toolkits have this handy. Use an obscure drive for security installations.

Shep
11-05-2016, 07:33 AM
[Reserved for future expansion]

Shep
11-05-2016, 07:33 AM
[Reserved for future expansion]