Threads, broaching, deep holes

Bolts, screws and nuts are one of the most common assembly methods in blacksmithing precisely because a threaded joint can be taken apart again — unlike a welded or soldered joint. Understanding the thread system and choosing the right clamping element is therefore as much part of the craft as being able to weld a seam.

§The metric thread system

In Denmark and the EU you cannot work freely with refrigerant. The person who services installs or empties systems with certain refrigerants must have a personal certificate and the company must be authorized to do so. The certificate shows you can handle refrigerant with minimal leakage — prepare systems test for leaks connect equipment and recover correctly. It is a part of your professional identity not a piece of paper for the drawer.

§Designation and tolerance

A thread fit

• 01Hex bolts and hex nuts for common construction
• 02Unbrako bolts where space is tight or appearance must be neat.
• 03PLACEHOLDER_82
• 04GF1 — broad introduction (typical for students directly from lower secondary).

§Pre-tension and clamping torque

A bolted joint's strength depends not only on the thread's dimension but also on how much it is tightened — the preload. Too little preload can loosen the joint under load, while too much can overload the bolt material or the overall structure. Many designs therefore specify a particular tightening torque to be observed with a torque wrench, rather than tightening 'by feel'.

§Protection against accidental loosening

Vibrations, temperature fluctuations and repeated stress can over time cause a threaded connection to loosen. For exposed connections, there are therefore a number of safety methods — lock nuts with built-in friction lock, spring washers, thread sealant and in some cases split pins or lock plates. The choice depends on how critical the connection is and what loads it experiences during operation.