Self-tapping screws

73.18 - Screws?bolts, nuts, coach screws, screw hooks, ri~ets,cotters, cotter-pins, washers (includmg spring washers) and similar articles, of iron or steel (+). - Threaded articles : 73 18.11 - - Coach screws 73 18.12 - - Other wood screws - - Screw hooks and screw rings 73 18.14 - - Self-tapping screws 73 18.15 - - Other screws and bolts, whether or not with their nuts or washers 7318.13 - - Other - Non-threaded articles : 7318.21 - - Spring washers and other lock washers 73 18.22 - - Other washers 73 18.23 - - Rivets 73 18.24 - - Cotters and cotter-pins 7318.29 - - Other 7318.19 (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. r Bolts and screws for metal are cylindrical in sha e, with a close and on1 slightly inclined thread; they are rarely pointed, and may have slotte heads or heads adapted or tightening with a spanner or they ma be recessed. A bolt is designed to engage in a nut, whereas screws for metal are more usuaKly 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 untheaded. B The heading includes all types of fastening bolts and metal screws re ardless of shape and use, f including U-bolts, bolt ends (i.e., cylindrical rods threaded at one en ), 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 tapped throughout but are sometimes blind. Lock nuts (usually thinner and castellated) They are usually butterfly nuts, etc. 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 cuttin thread since the have to bite their own way into the material. Further, wood screws almost a ways have slotte or recessed heads and they are never used with nuts. k 2' 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 closlng mechanisms, etc.) (Chapter 84). (d) Piano pegs and similar threaded parts of musical instruments (heading 92.09). (B) SCREW HOOKS AND SCREW lUNGS These are used to suspend or fix other objects and differ fiom the hook-nails of the preceding heading only in that they are threaded. (C)RIVETS Rivets differ from the oods described above in that they are non-threaded; they are usually cylindrical with round, fat, 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 ins are used for similar urposes but are usually larger and more solid, they may be desi ed, 11 e cotter-pins, to pass Lough holes (in which case they are often wedgeshaped), or or fitting into grooves or slots cut round the shaR, spindle, etc., in which case they may be of various shapes such as horseshoe or conical. F % Circlips are produced in different form ranging from a simple ring with a ga to more complex shapes (with eyelets or notches to facilitate application by means of speci 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 arts to be fixed to protect the latter. They may be plain, cut, split (e.g., Grower's spring washersf curved, cone shaped, etc.