RcTek : Information & Resources for the Model Car Racer

Fixings & Fasteners - Threaded Fastener Information

This section of the RcTek site is devoted to informing the radio controlled model car racer about the various Fixings & Fasteners that are used in remote controlled model cars.

In this article we have information for the model racer about threaded fasteners, how to measure them and the difference between a bolt and a set screw.

Basic Thread Terminology

Thread Identification

Threaded fasteners have differences in what is called their thread form, which is how many ‘teeth’ that they have for a given length of the threaded portion.

In the diagram on the right the ’teeth’ are called the threads (one thread is coloured yellow) and the distance between them is called the pitch (marked P).

The diameter (marked D) is the other important figure in the thread equation.

Different types of threads also have different thread angles (the angle between the ‘valleys’ of the threads) but the vast majority of radio controlled cars available today use only metric type threads.

Fastener Head Alignment

Screw and Bolt Heads

Threaded fasteners with different shaped heads will align themselves differently to the surface they are screwed into. This has to be remembered when buying fasteners as the length is based upon this alignment.

The image on the left shows the differences with alignment of various types of threaded fasteners.

As you can see they each sit at a different height relative to the surface into which they are screwed.

Measuring Fasteners

Fastener Length Determination

Fastener Length Determination

As mentioned above, the type of head a fastener has affects the length of fastener that you would specify when buying replacements for your radio controlled car. The diagrams below show both the correct and incorrect way to measure and specify fasteners.

The diagram on the right shows two different types of screws which are the same overall length. Because one is a countersunk screw and the other is a hexagonal headed screw, they cannot be directly compared by measuring their lengths. By studying the diagram above you will see that the countersunk screw would go further into the surface that it was screwed into.

The diagram on the left shows two different headed screws that have the same effective length, although their overall length is different. Both of these screws would penetrate the surface into which they were screwed by the same amount.

Bolt or Set Screw?

Threaded Bolt

Threaded Set Screw

This is a question that is often asked (especially when I am behind someone in a queue at the fastener suppliers!!).

The images to either side show the difference between a Bolt (left) and a Set Screw (right).

The difference is clear to see, the set screw is threaded all the way to the head, whilst the bolt isn’t.

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© 2001, 2009 by Darren Burnhill