In this exclusive extract from NBS Shortcuts , written by noted industry figure Austin Williams, we discuss the difference between fixings and fastenings.
When is a fixing not a fixing? When it's a fastener? Well not really, sometimes they can be one and the same thing. The best definitions are as follows:
- Fixing is the act of holding and securing an object in place (sometimes called the fixing method); and
- Fastener is the holding down and securing connectors used for fixing (sometimes called the fixing device).
The confusion arises because "fixing" is a gerund - that is, it can act as a verb or a noun - and so it helps to insist on its use as a verb only, where possible. Once it becomes used interchangeably, as it invariably is, the meaning can become confused. Using the word "fastener" is a way of clarifying this difference.
With this differentiation in mind, "fixings" describes a system for holding and securing components together or into place. For example, where a joist is nailed into a joist hanger with additional lateral restraint straps, then the "fixings" represents the complete system of straps, connectors, etc, whereas the 'fasteners' would be the nails. In the event of simple fixing (verb), where maybe a rafter is skew nailed to a wall plate, then "the fastener" is the "fixing" (noun), but as suggested above, it would be clearer to specify the fastener as the nail and the "fixing" as the nail centres. That's cleared that up. Except to say that the threaded part of a screw fastener is actually known as the fastening...
Anyway, this article provides an introduction to the various types, functions and uses of some of the huge range of nails and screw fixings. It will focus on common scenarios (wood screws, for example) and common tasks to which they are best suited.
Wire nails date from the late 19th century. Before that, "cut nails" were common, punched out, or guillotined, from a flat plate of rolled iron.
Nails, staples, wood screws, coach screws, bolts are all variants of dowel fasteners. The Timber Research and Development Association (TRADA) point out that all of them may be used for laterally loaded connections, but for axially loaded connections, only nails, screws and bolts are normally used. As such, nails are normally required to resist just the shear forces at the interface (or possible interstice) between two or more joined materials.
The Construction Information Service suggests that BS 1210: 1963 Specification for wood screws is "obsolescent but still relevant", predominantly because many of the referenced British Standards are obsolete.
To comply with the standard, all screws must have a minimum tensile strength of 550 N/mm² - which excludes coach screws - and have a shank diameter greater than 10 mm. In order to address some of these issues, a new suite of British Standards for screws (BS 1580: 2007) has just been released... although there is still no European Standard.
When comparing the jointing performance of fasteners of equivalent diameters:
- Nails generally have the advantage in terms of lateral load-carrying capacity
- Screws have better axial withdrawal resistance
- Dowel joints, in the form of timber dowels or through bolts, provide significantly higher load carrying capacity.
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The full text of this NBS Shortcut is exclusively available as part of a subscription to NBS Building Regulations .
NBS Shortcuts is a new series of illustrated "how-to" articles and guides, covering a wide range of practice, regulatory and design guidance. The easy to follow text and detailed hand-drawn graphics will aid any building designer. They are available online as part of your subscription to NBS Building Regulations.