Discovery II
GENERAL INFORMATION
03-12
Self-locking bolts and screws
Self-locking bolts and screws, i.e. nylon patched or
trilobular thread can be re-used providing resistance
can be felt when the locking portion enters the female
thread.
Nylon patched bolts and screws have a locking agent
pre-applied to the threads. They are identified by the
presence of a coloured section of thread which
extends for up to 180
°
around the thread.
Trilobular bolts (i.e. Powerlok) have a special thread
form which creates a slight interference with the
thread of the hole or nut into which it is screwed.
DO NOT re-use self-locking fasteners in critical
locations (e.g. engine bearings, flywheel). Always
use the correct replacement self-locking nut, bolt or
screw.
DO NOT fit non self-locking fasteners in applications
where a self-locking nut, bolt or screw is specified.
Nut identification
A nut with an ISO metric thread is marked on one
face or on one of the flats of the hexagon with the
strength grade symbol 8, 12, or 14. Some nuts with a
strength grade 4, 5 or 6 are also marked and some
have the metric symbol M on the flat opposite the
strength grade marking.
A clock face system is sometimes used as an
alternative method of indicating the strength grade.
The external chamfers or a face of the nut is marked
in a position relative to the appropriate hour mark on
a clock face to indicate the strength grade.
A dot is used to locate the 12 o'clock position and a
dash to indicate the strength grade. If the grade is
above 12, two dots identify the 12 o'clock position.
When tightening a slotted or castellated nut, never
loosen it to insert a split pin except where
recommended as part of an adjustment. If difficulty is
experienced, alternative washers or nuts should be
selected, or the washer thickness reduced.
Where bearing pre-load is involved, nuts should be
tightened in accordance with special instructions.
