Select one of the subjects below to find the answer to some of the most frequently asked questions. If you can't find an answer to your question here, please send us an email from our enquiry form and one of our staff will promptly answer your question by email.



Q. What is the difference between a fastener and a fixing?
A. A fastener joins together two existing elements or parts and a fixing attaches a moveable element to a fixed one. This is only a general rule and there are many exceptions and the terms are often used interchangeably. For example, a wood screw is a fastener but is often used as a fixing.
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Q. How are fasteners classified?
A. fasteners are either:
  • threaded e.g. nuts, bolts, screws and studs
  • non threaded e.g. nails, rivets, pins and washers
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Q. What factors influence the choice of fastener?
A. factors include:
  • function
  • properties
  • in-place cost
  • requirements of the fastener
  • method of assembly
  • the parts to be assembled
  • method of integration into the assembly process
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Q. Why are there so many different types of thread?
A. In the 19th century each industrialised company adopted its own thread standards. In Britain Sir Joseph Whitworth introduced what is now known as the British Standard Whitworth thread (BSW) and the fine pitch series became known as British Standard Fine thread (BSF), both BSW and BSF are now obsolete.

Similar work was carried out in the US by William Sellers. In 1948 the US, Britain and Canada established the Unified series now generally known as UNC (coarse pitch) and UNF (fine pitch). Unified threads are commonly used in the automotive, chemical and agricultural industries.

European threads are based upon the German DIN standards and are Metric coarse pitch and Metric fine pitch. Metric fasteners have slightly shorter pitch (distance between threads) than the imperial equivalent.
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Q. How do I specify a fastener?
A. The exact specification of a fastener consists of:
  • Generic dimensional standard for the fastener required - generally DIN standards but British Standards such as BS916 (black bolts & nuts) are also used
  • Head style and drive - necessary when using British Standards but often detailed in the DIN standard
  • Thread type
  • Diameter of the fastener (shank diameter)
  • Length of the fastener (may be overall length or length under the head depending upon the dimensional standard)
  • The decorative or protective finish required.
Therefore the specification for a hexagon headed bolt with a half inch shank, three inched long under the head with a unified fine pitch thread and no finish is:

1/2UNF x 3 Din 931

If metric dimensions are specified a course thread will be supplied by default. If a fine pitch thread is required this must be indicated after the diameter. A countersunk slotted head machine screw, thirty millimetre overall length, eight millimetre diameter with a fine pitch thread plated in bright zinc.

M8 x 1.0 x 30 Din 963 BZP.

However, the standards are so well known throughout the fastener industry that a description of the fastener, instead of the standard number, is nearly always sufficient. For example:

M10 x 50 Socket Set Screw ZYP.
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Q. How can I get more detailed information on the dimensions and performance of fasteners and fixings?
A. The easiest way is to ask us. We hold a huge technical library of standards and manufacturers specifications. Just click on the Contact RSR button and we will be happy to help.
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Q. How can I make these savings for my business?
A. Click here to find out.
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