Hey there! Nedzigon's back! How many different kinds of screws can you name? There are all kinds, from bolts to machine screws, tapping screws, nuts, and more. Today we'll talk about several of these, in particular the metric coarse thread types frequently used for machinery.
Metric screw standards
Metric screws are the most commonly used screws in the world, and come in coarse thread and fine thread versions.
Coarse screw threadThere are all kinds of sizes and materials of coarse screw threads in circulation, and they are economical, making them the most used screws.
Fine screw threadThe pitch of fine screw threads is finer than the coarse pitch type, so they are used when more precise adjustments are needed.
The large effective sectional area allows them to be tightly fastened and makes them unlikely to loosen. However, galling and seizing can easily occur when fastening due to the large amount of friction.
There is a table with the reference dimensions on another page, so take a look at that.
Loosely defining "bolts" versus "machine screws"
Hex head screw
General bolts that can be fastened using a wrench. Types with flanges to help prevent loosening are also available.
Hex socket head cap screws
These bolts have a hole in the head and are also often called cap screws. A hex wrench is used for fastening.
Hexalobular socket head cap screws
The shape allows minimal damage from tools compared to hex hole or cross-recessed hole types. They are used for repeated use at a high tightening torque. Machine screws are also available.
Machine screw types
Pan head machine screws
General screws with a head shape resembling a pan.
Flat head machine screws
These screws have a flat shape that fastens flush into the mounting surface.
Truss Head Screws
They have a larger bearing surface than pan head machine screws, for firmer fastening.
Next, I will introduce the different recess types for machine screws.
Called Phillips screws, these are the most common shapes. The tool is unlikely to slip when fastening and they can be secured tightly, which is why apparently more than 90% of all screws today have this cross-recessed shape.
These are also called flathead screws. The first screws invented were these slotted screws that could be machined easily just by adding a groove. They are still used today in areas easily dirtied. If cross-recessed types encounter dirt, the socket may become clogged, preventing their removal. Slotted types enable this dirt to be scraped out.
There are many more ways to classify screws in greater detail, but that is a story for another day.
That's all for today!