Camout: The rounding out of a drive system by point contact stress between a driver bit and the recess in a fastener during installation or removal due to torsional force required to tighten or loosen a screw.

Counterbored Hole: When a flush fit or level surface is desired when installing a fastener, just enough material is removed from the surface with a conical shaped drill bit to create a perpendicular recess for the fastener head to fit in fully when installed.

Countersunk Hole: A cylindrical hole created with an end mill tool that removes just enough surface material to create a recess for a fastener head with a flat underside to fit in fully to produce a flat or unhindered surface.

Head Diameter: The largest diameter of a shoulder screw; typically 30% to 50% larger than the shoulder diameter. May feature a smooth, machined finish, or knurled head.

Head Height: Shoulder screws tend to have a head height equal to 1/2 the diameter of the head. Low and ultra-low head profiles are also available, though they are typically manufactured with either a slotted drive style or are hex-headed.

Hex Head: A screw or bolt with a hexagonal head that can be installed with an open ended or socket style wrench that allows greater torque to be transferred to tighten or loosen the fastener.

Hex-Socket Head: Also known as a socket head cap screw, socket screw, or Allen bolt, a socket head cap screw is a fastener with a drive system with a recessed hexagonal drive hole in the head that can be installed or removed with a 6-sided hexagonal driver bit or Allen key.

Hoop Stress: Pressure generated during installation as a result of over-torquing a fastener with a perpendicular head in a counterbored hole that can result in the splitting or deformation of surface material.

Knurled Head: A series of small ridges or beads on a metal surface to aid in gripping. Ex. the serrated edge of a coin.

Lengthening Shim: Thin, washer-like metal discs that quickly increases the effective length of a bolt shaft when placed over the threaded end of the bolt against the bolts shoulder.

Major Diameter: The largest diameter of a screw thread measured at the crest of a male thread and at the root of a female thread.

Minor Diameter: The smallest diameter of a screw thread measured at the root of a male thread and at the crest of a female thread.

Precision Ground Bar Stock: center ground cold finished steel bar with a high degree of accuracy for straightness, roundness, and smooth surface finishes. It is manufactured from tool steel and is commonly used to produce highly accurate tools and dies with tight tolerances

Shortening Shim: Thin, washer-like metal discs that shorten the effective length of a bolt when placed around the threads or shoulder and under the head of a bolt before inserting it into a hole.

Swarf: Chips or small pieces of waste metal, wood, or plastic resulting from subtractive manufacturing processes.

Thread Cutting (Cut Threads): A process for forming screw threads. Threads are formed by using a cutting tool to remove material from a blank to form a thread. Cutting threads is highly precise compared to rolling threads as there is no deformation of material or reduction of thread diameter during production. Well suited for small runs, tapered threads, or threading up to a shoulder.

Thread Rolling (Rolled Threads): A process for forming screw threads. Threads are formed by pressing a shaped thread rolling die against a blank. Thread forming by rolling produces no swarf, and less material is required because the blank size starts smaller than a blank required for cutting threads. Rolled threads can be distinguished from cut threads because the threads have a larger diameter than the blank rod from which they have been made.

6 Lobe (Torx®-style) Drive: A drive system that virtually eliminates camout and extends tool life as the 6 Lobe design recess completely encloses the drive bit, minimizing tool slippage, allows torque to spread over a broader surface as 6 lobe sockets have a 15º drive angle (vs. the 60º drive angle of standard hex sockets and 45º drive angle of cruciform (Phillips) screw heads).

Undercut (Shoulder-Neck): Material removed just under the head of a shoulder screw to a smaller diameter than the shoulder that allows the screw to mount flush against mating components during installation. The width of the undercut is included when measuring the shoulder length.