Screws are used to fasten things against one another.

Countersunk screws

The bottom of the head, as it connects to the body of the screw, can either be flat and sit flat on top of the material, or be countersunk (sv: försänkt) and sit flush with the surface of the material

An alternate use for a countersunk screw is to center something with a round hole against something else. However this risks putting strain on the screw head in a way that is probably not very good.

Slot

The slot determines what screwdriver is used to drive the screw and how good a grip the intended screwdriver gets.

Flat: just a flat screwdriver. Poor grip. Pretty uncommon in this day and age.
Cross: more fancily called a Phillips, it’s a plus-sign. Probably the most common slot.
Pozidriv: a cross with a smaller cross rotated 45 degrees inside. Looks a lot like a regular cross, but grip will be lacking if using one. Deceptive little bastards.
Hex: a hexagon! Usually driven with an allen wrench, commonly found in IKEA furniture.
Torx: a hexagram! Relatively common and gets amazing grip.
Tri-point: looks like a Y. Used in equipment by manufacturers who resent the right to repair such as Nintendo.

Thread

Thread (sv: gänga) is the tracks around the screw that guide the screw into position. They are considered fine if their pitch is tight. Bolts are usually a lot finer than screws, as screws need to self-tap what they’re going into.

Screws vs bolts

Bolts (sv: bult) are usually distinguished from screws in that they are made to fit into a pre-tapped hole or a nut, whereas screws self-thread the hole, albeit not necessarily self-drilling. The technical disinction is a bit unclear, but that’s for Wikipedia to care about.

Nuts

A nut (sv: mutter) is what a bolt goes into!

Washers

A washer (sv: bricka) helps distribute force, preventing damage against both screw and material.

Metric screw standards

Metric screw standards, especially bolts, are labelled ‘MN’ e.g. M2, M10 where the number represents the diameter of the screw in millimeters. Although often omitted, a thread pitch can be specified in millimeters with a postfix of ‘×N’, e.g. ‘M2.5×0.5’. A length is often specified in marketing using the same format however, e.g. ‘M3×10’. If this was a thread pitch denomination, it would of course be a very silly one as M3 screws are usually not so long that there’d be more than one or two total revolutions of the thread.

Commonly used sizes are:

Pok3r-case 60% keyboards use M2.5 screws. It’s awful.

Funky screws

Hexagonal heads: Hex bolts usually have no slot and are instead turned with a wrench.
Train bolts: train bolts have a rounded head that cannot be gripped by mortal hands and no slot, meaning they can only be tightened by turning the nut.
Set screws: also known as grub screws (sv: stoppskruv), they are headless. They may have a slot in the body of the screw, usually a hexagonal one.

Screw (sv: Skruv)