FASTENERS

Introduction

Fasteners are a deceptively complex topic. Most of us unknowingly use fasteners incorrectly because we never take the time to learn about them. So this document is intended to provide a brief introduction to and overview of this diverse subject.

Some Basics

If you’ve complete my class, you know the topic of fasteners is an important one to me. Consequently let’s start with the basics covered in class:

Intro to Fasteners (the most thorough information you will likely receive on fasteners while at UF)

Fastener Facts (summary of Fasteners notes)

Fastener Reference Guide (fastener design guide)

Drill & Tap Chart (Tap Drill Sizes) (important handout used when designing parts requiring fasteners for joining)

How Bolts and Nuts Are Made (Video) (~ 4 min; very instructional)

Advanced Design Material

Fastener Design Manual (NASA) (a veritable treasure trove of fastener design data)

Includes:

1. Fastener materials (carbon steels: 55ksi, alloy steels: 300ksi; stainless: 70-220ksi; carbon and alloy steels should not be used below -65F)

2. Fastener coatings / platings (cadmium is the most common; LOTS of others; coating is limiting factor on max service temp.)

3. Lubricants (higher working temp, higher cost)

4. Corrosion (galvanic corrosion, stress corrosion, hydrogen embrittlement, cadmium embrittlement)

5. Locking methods (true locking nuts, serrated face fasteners, lockwiring, interfering thread, anaerobic adhesives)

6. Washers (purpose: distribute the clamping load; only locking type that works deform the surface of the part)

7. Inserts (used to provide a strong, wear resistant tapped hole in a weak material, as well as to repair stripped threads)

8. Thread types and classes (UNC, UNF, UNJC/F, UNR, UNK)

9. Fatigue loading

10. Fastener torque

11. Use guidelines and selection criteria for rivets

12. Use guidelines and selection criteria for lockbolts

Fastenal Fastener Technical Reference Guide (similar in scope the NASA manual linked above; another excellent resource)

DML Lab Resources Links

Taps, Dies & Threading (graphical discussion of different types of threading taps)

Damaged / Stripped Fastener removal (what to do when the inevitable happens …)

Thread Repair (what to do when things go really badly …)

Corrosion Resistance vs Strength

Typically, the more corrosion resistant a fastener, the weaker it is. 18-8 stainless steel is less corrosion resistant than 316 stainless (albeit cheaper).

Corrosion and Corrosion Resistance