FASTENER COMPONENTS. Chapter 1. Fastener Components Page 1

Transcription

1 An analysis of standard fasteners such as bolts and screws, reveals that all have certain characteristics in common. Further, their differences can be classified as shown in this chart. Each bolt and screw is in effect made up of a series of component parts. Thus the fasteners may have some or all of these: (a) a head; (b) a driving recess; (c) a shoulder; (d) an unthreaded shank; (e) a threaded shank; (f) a point; and (g) a slot. Certain Combinations of these components because of usage are considered standard. Others are non-standard, but nearly any combination can be readily produced. This analysis of fastener parts is presented in the hope that it will assist the user in understanding and specifying bolts and screws. Chapter 1. Fastener Components Page 1

2 BOLTS AND CAP SCREWS Hex Head Bolt standard head for machine bolts and screws. Has ample bearing surface for wrench tightening. Hex Head Washer same as hex but with washer section at base to protect work surface against wrench disfigurement. Used for machine screws, tapping screws. Also with slotted or phillips head. Flat Head Cap Screw or Machine Bolt flat countersunk bolt, often with slotted head. Socket Head Cap Screw fasteners with a hexagonal socket or recess. Internal wrenching screws and bolts are used in a tapped and counterbored hole. Flat Socket Head Cap Screw flat countersunk screw or bolt with a hexagonal socket or recess for internal wrenching. Square Head Bolt generous bearing surface for wrench tightening. Generally not considered standard for corrosion-resistant fasteners. Step Bolt used in joining resilient materials like wood or sheet metal to steel framework, this plain, oval head bolt has a square neck to prevent turning. Round Head Square Neck Carriage Bolt round head bolt with square neck. Generally used with resilient material such as wood or sheet metal. Elevator Bolt has thin circular head of extra large diameter. Square shoulder under head prevents turning when nut is applied. Used where wide, thin bearing surface is desired. Hanger Bolt wood screw threaded bolts on one end with gimlet point and have coarse pitch machine screw thread on other end. Center section is unthreaded. Connector Bolt used in the electrical industry for attaching contacts. T-Bolt used in the machine tool industry. T-head can be inserted in a T-slot in a tool bed. Page 2 Chapter 1. Fastener Components

3 BOLTS AND CAP SCREWS Oval Track used for railroads and electric railways for holding lengths of rail together. Elliptic and general purpose oval neck types are made in mushroom, round, and button head styles. Twelve Point Head Bolt a double hexagon head used extensively in the aircraft industry because of its superior adaptability to pneumatic wrenching. Available in bolts and machine screws. Plow Bolt used on farm machinery and heavy construction equipment. Lag bolt also called a lag screw, this hex (or square) head fastener has a 60 degree gimlet conical point for use in wood or in masonry. Oval Head Bolt a slotted oval headed bolt specified for flush mounted seating. Resembles machine screw but is designed for heavier duty applications. Wedge Bolt used for hanging marble fascia on buildings. Drilled Eye Bolt special eye bolt for use where closer tolerance, higher strength, as compared to bent eye bolt, is required. Provides smaller eye O.D. Often used for valves. Closed Eye Bolt, U Bolt, J Bolt, Right Angle Bolt partially threaded rods with special bent body shapes are used where a formed shank is required. STUDS AND THREADED ROD Double End Stud both ends threaded for standard nut assembly. Tap End Stud (Type A ) the tap-end stud is a headless fastener with one threaded end designed for semi-permanent installation in a tapped hole and another end threaded for standard nut assembly. Continuous thread stud (Type C ) Diameter and length as specified, threaded full length. Threaded Rod - continuous threaded rods, lengths are manufactured in various sizes. Chapter 1. Fastener Components Page 3

4 SET SCREWS Square Head Set Screws for high wrenching torque applications. The square has sharp, well-defined corners. Threads extend to the head. Headless Slotted Set Screws where flush surfaces are desired Screw can be driven below the surface of work. Socket Type Set Screws for internal wrenching. And where frequent disassembly or adjustment occurs. NUTS Heavy Hex Jam general purpose nut for heavy loads. Jam nut can be used with another jam nut (which is chamfered) for locking. Regular Hex Nut Full and Jam general purpose nut. Jam can be used with another jam nut for locking. Weld Nut used in applications similar to clinch nuts. Weld nuts, when properly welded, retain themselves to the parent material to a much greater degree than clinch nuts. Weld nuts require more sophisticated apparatus for their installation. Maintenance of welding equipment is of prime importance to ensure a good consistent weld. Hex Slotted Nut standard hex nut with slots milled across the flats of the face can be locked with cotter pin or safety wire inserted in drilled hole of bolt. Castle Nut solid hex base nuts have cylindrical crown with milled slots. Used for general purpose fastening or with cotter pin or wire through the slots. Cap Nut (Acorn Nut) Crown dome nut with blind tapped hole, generally used for appearance. Wing Nut where frequent disassembly for service or field adjustments required-threaded one-piece nut available in a number of tab styles. Square Machine Screw Nut a nut with flat bottom and flat top, used with machine screw for light and medium duty fastening applications. Page 4 Chapter 1. Fastener Components

5 NUTS Hex Machine Screw Nut all purpose nuts, assembled with machine screws for mass production applications. Hex machine screw nuts are chamfered. Knurled Nut where periodic manual assembly, adjustment and, or disassembly is required. The roughened surfaces makes easier fingering. WOOD SCREWS Round Wood Screws, Oval Wood Screws and Flat Wood Screws Gimletpointed screws are threaded to the tip to facilitate entry into wood, available with round, flat or oval head with slotted or Phillips driving recess. Wood screws are usually driven into drilled holes to avoid cracking the surface and are available in round, oval and flat head styles. RIVETS Round Head Rivet the most common rivet head, specified for most general applications. Flat Head Rivet head in a low, round & flat protruding type of head, not countersunk. Specified where a low head will solve design problem. Countersunk Head Rivet for flush surfaces applications. Angle of countersink on small diameter is 90 degrees, rivets one-half inch and over, 78 degrees. Tinners Rivet the larger head provides a greater distribution of load on light gage metal. Used principally in sheet metal work. Semi-Tubular Rivets essentially a solid rivet except that the lower section of the rivet shank, actually used in forming the clinch, is center drilled. This permits easy clinching when the rivet is struck by the riveting hammer. Blind Rivet a blind fastener which has a self-contained mechanical or other feature which permits the formation of an upset on the blind end of the rivet and expansion of the rivet shank during rivet setting to join the component parts of an assembly. Chapter 1. Fastener Components Page 5

6 WASHERS Flat Washer (SAE & USS) also called plain washers, these flat discs with center holes are applied under the head of the part to be tightened. Lock Washer Helical Spring to compensate for loss of tension between parts. To act as a thrust bearing assembly and/or disassembly of parts. Countersunk Finishing Washer generally used for appearance with a countersunk screw. External Tooth Lock Washer has somewhat greater locking action that internal tooth lock washer. Internal Tooth Lock Washer used where better appearance than with external tooth lock washer desired, at slight sacrifice in locking action. PINS & NAILS Common Nail, Boat Nail, and Escutcheon Pin common nail has flat, round head, escutcheon pin has round head, and boat nail has annular groves in shank. Cotter Pin round, split pin used as safety locking device, generally through a slotted or castle nut; through drilled hole in shank of bolt or screw. Dowel Pin widely used in machinery applications, these cylindrical pins are available both hardened and unhardened. Taper Pin where disassembly is expected, taper pin, which can be easily driven out of its sized hole is useful fastening element. Spring Pin has straight cylindrical sides with both ends chamfered, available in two basic types, reflecting slotted construction and coiled construction. Slotted type spring pins having a single wall and coiled type spring pins having multiple walls are formed or wrapped from basic strip stock to a diameter larger than basic and heat treated. Upon installation the pin diameters contract and the spring reaction against the sides of the hole tends to retain the pin. Page 6 Chapter 1. Fastener Components

7 DRIVE TYPES Square Phillips Combination Phillips/Slot Slotted Head Also referred to as combo Frearson Clutch Heat External Hexagon Internal Hexagon Hexagon Washer Head Tamper Proof External Torx Drive Also referred to as 6 lobe Tamper Proof Internal Torx Drive Also referred to as 6 lobe Tamper Proof Also referred to as one way slot Tamper Resistant Torx Drive HEAD TYPES Flat Head supplied to standard dimensions with an 80 degree to 82 degree angle (metric is 90 ) to be used where finished surfaces require a flush fastening unit. The countersunk portion offers good centering possibilities. Round Head the familiar head most universally used for general application. Good slot depth, ample underhead bearing surface and finished appearance are characteristic of this head. Oval Head fully specified as oval countersunk, this head is identical to the standard flat head but possesses, in addition, a rounded, neat appearing upper surface for attractiveness of design. Fillister Head the standard oval fillister head has a smaller diameter than the round head, but is higher with a correspondingly deeper slot. The smaller diameter head increases the pressure applied on the smaller area and can be assembled close to flanges and raised surfaces. Headed in counterbored dyes to insure concentricity, they may be used successfully in counterbored holes. 1 TORX is a registered trademark licensed by CAMCAR Division of TEXTRON INC. Chapter 1. Fastener Components Page 7

8 HEAD TYPES Binding Head (Straight Side) most generally used in electrical and radio work because of its identifying undercut beneath the head, which binds and eliminates fraying of stranded wire. Offers an attractive designed, medium-low head with ordinarily sufficient bearing surface. Not ordinarily recommended as a Phillips Recessed head see Pan Head for better functional design. Truss Head also known as oven head, stove head, and oval binding head. A low, neat appearing, large diameter head having excellent design qualities, and as illustrated can be used to cover larger diameter clearance holes in sheet metal where additional play in assembly tolerance is required. Lentil Head (also called trimmed heads) designed with a greater degree of countersunk and low oval portion, this head also has a smaller than standard head diameter. Generally used on thin moulding strips requiring counterbored self-centering facilities and neatness of finished product. Similar styles also known as Jackson Head and Dunbar Head have smaller heads with standard 82 degree counterbore. Pan Head provides a low, large diameter head, but with characteristically high outer edges along the outer periphery of the head where driving action is most effective. Recommended for such items as self-tapping screws and designs requiring high tightening torques. Slightly different head contour when supplied with Phillips Recess. See dotted line. Flat Fillister Head this head style was popular many years ago because it was easy to produce by milled-from-the-bar processes then in use. It has practically the same dimensions as a standard fillister head minus the oval section and is sometimes used in counterbored holes requiring flush finished surfaces. The use of the standard oval fillister shown above is recommended whenever possible. Holt Head (Patented) provides the perfect tamper-proof assembly. Theftproof decorative, yet inexpensive. Special drivers available for field removal or power driven assembly machines. Round Washer Head this design has the finished appearance of a conventional round head plus washer, and was originally created to provide extra large bearing surface under the head. The modern truss head (carried in stock) normally answers this purpose. When a larger head diameter is required this washer head designed is recommended. One-Way Head this ingenious, tamper-proof type of head, once assembled cannot be removed, yet is driven with a standard screw driver. Manufactured with amazing economy in production quantities, this simple design can frequently solve costly assembly problems. Page 8 Chapter 1. Fastener Components

9 HEAD TYPES Flat and Oval Heads (Undercut) this is the standard flat or oval head 80 degrees to 82 degrees (metric is 90 ) countersunk screw which has the lower one-third of the countersunk portion removed to facilitate production of extremely short lengths. As illustrated, it will fit a standard counterbored hole and is particularly adaptable to flush assemblies in this stock. Flat Head (100% Countersunk) this special flat head screw has been developed for applications requiring flush surfaces, and is recommended for use in soft materials, to distribute pressure over a larger and less angular surface. Very well adapted for use with thin aluminum, soft plastics, etc. Plumbers Head this head was developed many years ago for the plumbing trade. It offers a higher and slightly smaller diameter head than the standard round head to facilitate assembly and good solid tightening abilities. Modern designs recommend the use of the standard round heads. Square Shoulder Screws an adaptation of the standard carriage bolt design. Possesses a truss head on a square shank which resists rotation when located or driven into place. This square shoulder may also be staked into place as a permanent fastener. A great many varieties in all screw diameters are available in productive quantities. Round Shoulder Screws this style is supplied with a regular truss head but possesses a round shoulder larger in diameter than the outside of the thread. Often uses as a spacer between two sections or to provide bearing surface for rotating parts. Knurled Shoulder Screws a truss head on a round knurled shoulder make up the design of this part. It is used principally for locking purposes and may be molded into plastics or staked into metal. Shoulder length and knurled diameters can be varied to fit the application. Available in productive quantities. Fin Head Bolts a truss head supplied with either tow or four fins to lock screw threads against rotation in thin sections of plywood, etc. More satisfactory than the square shoulder design for applications of this type because of the larger surface area contacted by the fins. Indented Hexagon an inexpensive wrench head fastener made to standard hexagon head dimensions. The hex is completely cold upset in a counter bored die and possesses an identifying depression in the top surface of the head (Hex head machine screw). Indented Hexagon Washer Head produced in the same manner as the standard indented hexagon head but with a washer section at the base of the head to protect the finish of the assembly from wrench disfigurement, also provides larger bearing surface. Chapter 1. Fastener Components Page 9

10 HEAD TYPES Acorn Head this wrench type head has been designed for appearance, speed of assembly, and protection against wrench disfigurement of finished surfaces. Its familiar domed hex atop the washer section located quickly and easily with socket wrenches and can also be slotted for removal in the field. Hexagon Head (Trimmed) this is the standard type of wrench-applied hexagon head, characterized by clean, sharp corners trimmed to close tolerances. Recommended for general commercial applications, it is available in all standard patterns and in all thread diameters. (Hex head machine bolt). Square Head (Trimmed) the standard commercial head as applied to machine bolts. This trimmed, accurately dimensioned head is also available in all diameters of screws, and offers square, sharp corners plus extra generous bearing surface for wrench tightening. Hexagon Head (Finished) this standard trimmed hexagon head screw has the added feature of a washer under the surface of the head slightly smaller in diameter than the distances across the flats which protects the finished assembly against disfigurement by the rotation of the corners of the head. Also applies equal pressure on the circular washer surface. (Hex head cap screw). Seating Bolts this special combination of a countersunk square shoulder screw was developed for special applications requiring neat outside appearance combined with square shank locking features. Finishing washers may also be applied to this head to further enhance the appearance. Welding Screws the welding screw has been developed to provide a strong, permanent threaded fastener which becomes an integral part of the assembly. It utilizes the principle or projection welding by means of multiple lugs applied to various surfaces. Type U (Underlug) for general application. Assembles easily into prelocated holes and fully utilizes head strength. Top surfaces of head designed for efficient welding anode contact. Flat Head styles take full advantage of self-centering feature of the countersunk portion and provide a smooth, flush outer surface. Type T (Overlug) for applications requiring smooth, finished outer surfaces. Under surface of head is designed for perfect electrode contact. Page 10 Chapter 1. Fastener Components

11 POINT TYPES Die Point ( a header point) one of the lease expensive pointing operations applied at the time of heading. This operation provides an end chamfer starting with a diameter smaller than the root diameter of the thread. The minimum reduction of the point is approximately 10% below the maximum minor diameter with an included angle of 40 degrees to 50 degrees. Dog Point a straight pointed section reduced in diameter slightly below the root diameter of the thread usually extending in length about two-thirds the diameter of the thread. Recommended for ease in starting, to insure against stripping fine threaded products, and to increase efficiency along production lines. Rolled Point an efficient method of producing pointed long studs or long screws with and end chamfer similar to the Die Point. The last thread and a half is slightly cupped by the thread roll-over operation. Pinch Point (Rounded) an inexpensive method of applying a 60 degree lead-in point having a slightly rounded contour but with pinch-off marks on its surface. Used for aligning several sheets or assembling several parts requiring pilot action. Nail Point (Pinched) usually supplied with an approximate 45 degree included angle having a sharp point and slightly squared surface. Used for impinging or locking against wood or other soft material. Other degrees of included angle and sharpness also available. Cupped Point special cup section supplied on the end of the threaded member having a depression in the end to reduce the area in contact with the surface which increases its holding and locking power under pressure. Round Point a dome-like rounded surface applied to the end of a threaded member in order to offer pressure without disfigurement. Used for adjusting members where friction without cutting action is desirable. Cone Point a precision cut-pointing operation to provide any required included angle. Offers a smooth surface, accurate length, and a sharp point which can be produced to any desired contour to fit your particular requirements. Cut Points We illustrate a variety of tenon ends which can be supplied in the form of straight cut points wherein the diameter of the tenon end is substantially below the root diameter of the thread and a square abutment surface is required. As illustrated this style of point offers excellent bearing surface when assembled into prepared washers or other assemblies requiring free turning pressure surfaces, as in clamps, etc. Cut points can also be grooved for special locking rings, cupped for ease in riveting operations, or machined to other contours to meet your specific requirements. Chapter 1. Fastener Components Page 11

12 POINT TYPES Type 25 Point(also called BT) a thread cutting screw similar to Type 23 point except with coarse Type B thread. For plastics and other soft materials with large chip clearing and cutting edges. Self-Drilling with special drilling points lengths diameters that will drill through 1/4 metal. Eliminates all hole preparation drills faster than a drill. No punching, drilling or tapping required. Reduces die costs. Self-Drilling produces more secure sheet metal assemblies faster... used as self-drilling screw or driving thru pre-punched holes. Can be used with or without pilot holes. Positive rake forward cutting edge drills straight thru sheet metal at peak speed. Perfectly mated threads increase strip and back out pressures. TAPPING SCREWS Type A Point a thread forming screw for use in thin metal.015 to.050 thick. Used with drilled, punched or nested holes in sheet metal, resin impregnated plywood, asbestos combinations, among others. Not recommended for new design. Type B Point a thread forming screw for use in heavier metal.050 to.200 thick. Larger root diameter with finer thread pitch for light and heavy sheet metal non ferrous castings, plastics, impregnated plywoods, asbestos combinations, and other materials. Type AB Point a thread forming screw combining locating type point of Type A with thread size and pitch of Type B. Normal limitations of Type B apply. Type C Point a thread forming screw with either coarse or fine pitch machine screw thread and blunt tapered point. Eliminates chips and permits replacement with standard screw in the field. Higher driving torque required. Usable in heavy sheet metal and die castings. Type U Point a thread forming screw with high Helix thread for driving or hammering into sheet metal, castings, fiber or plastics for permanent, quick assemblies. Type F Point a thread cutting screw with machine screw thread with blunt tapered point, having multi-cutting edges and chip cavities. for heavy gauge sheet metal, aluminum, zinc and lead die castings, cast iron, brass and plastic. Type FZ Point (also type F) a thread cutting screw with a tapping screw thread with blunt tapered point and multi-cutting edges and chip cavities. For plastics, die castings, metal clad and resin impregnated plywoods, and asbestos. Type BF Point spaced thread Type B with blunt point and five evenly spaced cutting groves and chip cavities. Reduces stripping in brittle plastics and die castings. Good for long thread engagement, especially in blind holes. Faster driving than fine thread type. Page 12 Chapter 1. Fastener Components

13 TAPPING SCREWS Type BP Point same as Type B, but has a 45-degree included-angle, unthreaded cone point. Used for locating and aligning holes, or piercing soft materials. It is recommended type AB be used instead of BP. Type 1 Point (Type D) a thread cutting screw with single flute for general use. Produces fine or course standard machine screw thread for field replacement. Type 17 Point (also AT or ABT) a thread cutting screw for wood with a coarse tapping screw thread and a special long sharp point fluted to capture chips. Type 23 Point (Type T) a thread cutting screw in coarse or fine thread series offering maximum thread cutting area and excellent chip cleaning, with minimum tightening torques. Chapter 1. Fastener Components Page 13