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Heading 7318 : Screws, bolts, nuts, coach screws, screw hooks, rivets, cotters, cotter-pins, washers (including spring washers) and similar articles, of iron or steel.
(A) SCREWS, BOLTS AND NUTS
Bolts and nuts (including bolt ends), screw studs and other screws for metal, whether or not threaded or tapped, screws for wood and coach-screws are threaded (in the finished state) and are used to assemble or fasten goods so that they can readily be disassembled without damage.
Bolts and screws for metal are cylindrical in shape, with a close and only slightly inclined thread; they are rarely pointed, and may have slotted heads or heads adapted for tightening with a spanner or they may be recessed. A bolt is designed to engage in a nut, whereas screws for metal are more usually screwed into a hole tapped in the material to be fastened and are therefore generally threaded throughout their length whereas bolts usually have a part of the shank unthreaded.
The heading includes all types of fastening bolts and metal screws regardless of shape and use, including U-bolts, bolt ends (i.e., cylindrical rods threaded at one end), screw studs (i.e., short rods threaded at both ends), and screw studding (i.e., rods threaded throughout).
Nuts are metal pieces designed to hold the corresponding bolts in place. They are usually tapped throughout but are sometimes blind. The heading includes wing nuts, butterfly nuts, etc. Lock nuts (usually thinner and castellated) are sometimes used with bolts.
Blanks for bolts and untapped nuts are also included in the heading.
Screws for wood differ from bolts and screws for metal in that they are tapered and pointed, and they have a steeper cutting thread since they have to bite their own way into the material. Further, wood screws almost always have slotted or recessed heads and they are never used with nuts.
Coach screws (screw spikes) are large wood screws with square or hexagonal unslotted heads. They are used to fix railway lines to the sleepers and to assemble rafters and similar heavy woodwork.
The heading includes self-tapping (Parker) screws; these resemble wood screws in that they have a slotted head and a cutting thread and are pointed or tapered at the end. They can therefore cut their own passage into thin sheets of metal, marble, slate, plastics, etc.
The heading also covers all unpointed drive screws (or screw nails), and also those which are pointed provided that their heads are slotted. Drive screws have very steep threads and are often driven into the material with a hammer, but often can be withdrawn only by use of a screwdriver.
This group excludes : (a) Pointed screw-nails with unslotted heads (heading 73.17). (b) Screw stoppers (heading 83.09). (c) Threaded mechanisms, sometimes called screws, used to transmit motion, or otherwise to act as an active part of a machine, (e.g., Archimedian screws; worm mechanisms and threaded shafts for presses; valve and cock closing mechanisms, etc.) (Chapter 84). (d) Piano pegs and similar threaded parts of musical instruments (heading 92.09). (B) SCREW HOOKS AND SCREW RINGS
These are used to suspend or fix other objects and differ from the hook-nails of the preceding heading only in that they are threaded. (C) RIVETS
Rivetsdiffer from the goods described above in that they are non-threaded; they are usually cylindrical with round, flat, pan shaped or countersunk heads.
They are used for the permanent assembly of metal parts (e.g., in large frameworks, ships and containers).
The heading excludes tubular or bifurcated rivets for all purposes (heading 83.08) but rivets which are only partly hollow remain classified in this heading. (D) COTTER-PINS AND COTTERS
Cotter-pins, usually of bifurcated form, are used for fitting in holes in spindles, shafts, bolts, etc., to prevent objects mounted thereon from moving along them.
Cotters and taper pins are used for similar purposes but are usually larger and more solid, they may be designed, like cotter-pins, to pass through holes (in which case they are often wedge-shaped), or for fitting into grooves or slots cut round the shaft, spindle, etc., in which case they may be of various shapes such as horseshoe or conical.
Circlips are produced in different forms ranging from a simple ring with a gap to more complex shapes (with eyelets or notches to facilitate application by means of special pliers). They are always intended, whatever their shape, to be placed in a groove, either around a shaft or inside a cylindrical bore, to prevent the relative movement of parts. (E) WASHERS
Washers are usually small, thin discs with a hole in the centre; they are placed between the nut and one of the parts to be fixed to protect the latter. They may be plain, cut, split (e.g., Grower's spring washers), curved, cone shaped, etc. Subheading Explanatory Notes. Subheading 7318.12
The term "screw" does not cover screw hooks and screw rings; these are classified in subheading 7318.13. Subheading 7318.14
This subheading covers the Parker (self-tapping) screws described in Explanatory Note to heading 73.18, Part (A), eighth paragraph.
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clhs@clhs.co.kr 
070-4214-8300