Bolts and screws
Fastener head types are either of hexagonal, Torx or splined design, with internal and external versions of each type. The conventional slotted or Phillips head design is used for certain screws. Bolt or screw length is always measured from the underside of the head to the end of the item.

Certain fasteners have a tensile marking on their heads, the higher the marking the stronger the fastener. High tensile fasteners generally carry a 10 or higher marking. Never replace a high tensile fastener with one of a lower tensile strength.

Washers
Plain washers are used between a fastener head and a component or to spread the load when torque is applied. Plain washers can also be used as spacers or shims in certain assemblies. Copper or aluminium plain washers are often used as sealing washers on drain plugs.

The split-ring spring washer works by applying axial tension between the fastener head and component. If flattened, it is fatigued and must be replaced. If a plain washer is used on the fastener, position the spring washer between the fastener and the plain washer.

Serrated star type washers dig into the fastener and component faces, preventing loosening. They are often used on electrical earth (ground) connections to the frame.

Cone type washers (sometimes called Belleville) are conical and when tightened apply axial tension between the fastener head and component. They must be installed with the dished side against the component and often carry a OUTSIDE marking on their outer face. If fattened, they are fatigued and must be replaced.

Tab washers are used to lock plain nuts or bolts on a shaft. A portion of the tab washer is bent up hard against one flat of of the nut or bolt to prevent it loosening. Due to the tab washer being deformed in use, a new tab washer should be used every time it is disturbed.

Wave washers are used to take up endfloat on a shaft. They provide light springing and prevent excessive side-to-side play of a component. Can be found on rocker arm shafts.

 

Conventional plain nuts are usually six-sided. They are sized by thread diameter and pitch. High tensile nuts carry a number on one end to denote their tensile strength.

self-locking nuts either have a nylon insert, or two spring metal tabs, or a shoulder which is staked into a groove in the shaft - their advantage over conventional plain nuts is a resistance to loosening due to vibration. The nylon insert type can be used a number of times, but must be renewed when the friction of the nylon insert is reduced, ie when the nut spins freely on the shaft. The spring tab type can be reused unless the tabs are damaged. The shouldered type must be renewed every time it is disturbed.

Split pins (cotter pins) are used to lock a castellated nut to a shaft or to prevent slackening of a plain nut. Common applications are wheel axles and brake torque arms. Because the split pin arms are deformed to lock around the nut a new split pin must always be used on installation - always fit the corret size spit pin which will fit snugly in the shaft hole. Make sure the split pin arms are correctly located around the nut.

R-pins (shaped like the letter R), or slip pins as they are sometimes called, are sprung and can be reused if they are otherwise in good conditon. Always install R-pins with their closed end facing forwards.

Pictures, top: Ring spanner on a shaft; bottom: impact driver on a Phillips-head screw.

Internet:
http://www.metalgrip.com
http://www.nutty.com
http://www.premiertools.co.uk/
http://www.maclean-nj.com/toolboy.htm
http://www.diyfaq.org.uk/fasteners/fastener.html#bolts

 

Diameter of a male thread (screw, bolt or stud) is the outside diameter of the threaded portion. Most motorcycle manufacturers use the ISO (International Standards Organisation) metric system expressed in millimeters, eg M6 refers to a 6 mm diameter thread. Sizing is the same for nuts, except that the thread diameter is measured across the valleys of the nut.

Pitch is the distance between the peaks of the thread. It is expressed in millimeters, thus a common bolt size may be expressed as 6.0 x 1.0 mm (6 mm thread diameter and 1 mm pitch). Generally pitch increases in proportion to thread diameter, although there are always exceptions.

Thread diameter and pitch are related for conventional fastener applications and tables (Tabellenbuch Metall) can be used as a guide. Additionally, the AF (Across Flats), spanner or socket size dimension of the bolt or nut is linked to thread and pitch specification. Thread pitch can be measured with a thread gauge.

The threads of most fasteners are of the right-hand type, ie they are turned clockwise to tighten and anti-clockwise to loosen. The reverse situation applies to left-hand thread fasteners, which are turned anti-clockwise to tighten and clockwise to loosen. Left-hand threads are used where rotation of a component might loosen a conventional right-hand thread fasteners.

Your job
1) Translate the text into German.

2) Compile a list of the 'working-rules' mentioned in the text.

3) Compare this article with the corresponding chapter in your 'Fachkunde Metall'. Can you find any grave discrepancies?

4) Explain the tensile strength denotation of bolts and nuts.

5) When do we use a torque wrench to fasten a bolt or nut?

6) What is torque? Make a sketch to help explain it.

7) How can you loose seized, corroded bolts and nuts?

8) How can we reenforce threads in soft metals like aluminium or copper?

9) Compile a list of tools we need to work on all types of fasteners.

10 ) What means prevent a screw or nut from getting loose and lost?