12. Pulley blocks for fibre ropes
12.1. General provisions
12.1.1. (1) A pulley block for use with rope consisting of man-
made or natural fibre should have either a cast housing, or side and
partition plates and straps of steel or of wood suitably reinforced
with steel or aluminium straps.
(2) Except in the case of a cast housing, the side. straps should be
adequately and properly secured to the head fitting.
12.1.2. (1) The diameter of the sheave(s) measured at the
bottom of the groove should not be less than 5.5 times the rope
diameter it is designed for.
(2) The rope groove should have a depth of not less than a third
of the diameter of the rope, the radius of the groove being not less
than 1 mm greater than half the diameter of the rope.
12.1.3. As a general rule, the block should not be fitted with
more than three sheaves and a becket, or four sheaves if the block is
without a becket.
12.1.4. Provision should be made for the lubrication of all
metal bearings and swivel head fittings and, where necessary, any
12.2. Safe working load
12.2.1. The safe working load of the block should be assessed
on the basis of use with best-grade manila rope.
12.3. Compliance with other requirements
12.3.1. The block should comply with the requirements of sub-
paragraphs 4.2.1(e), 6.4.5(d), and 6.4.7(1) and (2), and as far as
possible with section 6.5.