Grub Screw:

A Grub screw, also known as a blind screw or a set screw, generally used to secure an object within or against another object, usually without using a nut. The most common examples are securing a pulley or gear to a shaft. Set screws appear with a variety of tip (point) types. The different shaped tips have different properties that engineers can utilize. If an engineer were to use a detent to ensure proper nesting of the screw, they might choose to use a cone point type of screw. One might often need to use a flat point when the screw must press perfectly flat against a surface. The most common type is the cup point. This type works well because the surface is rounded so that a small surface area is in contact, but it does not have extremely high stress at one point like that of a cone point. Durability studies show that the cup point offers superior resistance to wear while maintaining a strong grip.Knurled cup points offer the added advantage of a locking action (similar to that of a serrated lock washer) that prevents the screws from working loose in high-vibration applications. Common points include the following:

• Flat point
• Domed point
• Cone point
• Cup point
• Extended point (pilot point, dog point)

General:

However, they most often do not have heads and consist entirely of threaded shaft. The ‘M’ here basically signifies metric units – an M8 x 12mm grub will be 8mm wide at the major (outer) diameter of the thread, and 12mm long. Similarly, an M5 x 150mm set will be 5mm in diameter across its threaded section, and 150mm long from head to end. Turn the grub screw clockwise slightly with either an Allen wrench or flat-head screwdriver, depending on the screw. When the screw moves, turn the screw counterclockwise to remove it from the part. The movement clockwise, as if tightening, sometimes breaks the seal any rust may have on the screw.