Threaded Fasteners

Threaded fasteners used in FS are most typically made of steel but are sometimes also made of stainless, titanium, or aluminum.

Standards

There are two main threaded fastener standards: metric and inch. Within these two categories lay additional standards set by various organisations. These standards may are often intercompatible but can differ in head size, strength, alloy, coating, pitch, and local avaliability.

Metric

Metric screws are listed in the following way:M6x25 x 1mm Class 8.8. The M6 referes to the major diameter being 6mm, 25: the shaft length is 25mm, and the pitch is 1 thread per 1mm. A class 8.8 bolt is a medium strength steel bolt with a tensile strength of about 800MPa and about 80% of that being the yield strength.

Inch

Inch screws are listed in the following way:1/4-20 x 1 Grade 5. The 1/4 is the major diameter of 1/4in, a thread pitch of 20 threads per inch, and a length of 1in. A grade 5 bolt is a medium strength steel bolt with a tensile strength of about _ksi and a yield strength of _ksi.

SAE

[grades, charts, etc...]

Screw Types

Socket Head

aka Allen® head

Quarter Turn

A quarter turn is a specialty fastener that allows quick installation and removal of body panels

. They also may be refered to by the trade name Dzus fastener.

Nut Types

Locknut

Locknuts resist loosening. Other methods can be used to resist loosening: lock washers

, safety wire, locking adhesive, or design.

Distorted Thread

Jet/K Nut

great in high temperature environments. see brakes

Fastener Characteristics (how to choose)

• Initial Tensioning
• Initial Tightening Force
  • Brings bolt close to "proof load"
• Deformation of threads (pic)
• Maintenance schedule

Further Reading

• NASA Fastener Design Manual
• Carroll Smith's Screw to Win