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Major Diameter: The largest diameter of the threadMinor Diameter: The smallest diameter of the threadPitch: Distance between two threads (mm) or no of threads per inch.
Pitch Diameter The diameter of an imaginary cylinder passing through the threads to make equal the widths of the threads and the widths of the spaces cut by the cylinder. Lead The distance a screw thread advances axially in one turn. Angle of thread The angle included between the sides of the thread measured in a plane through the axis of the screw
Crest: The top surface joining the two sides of the threads.Root: The bottom surface joining the sides of two adjacent threads. Side: The surface of the thread that connects the crest with the root.
Axis of screw: The longitudinal center line through the screw. Depth of thread: The distance between the crest and the root of the thread measured normal to the axis. Form of thread: The cross section of thread cut by a plane containing the axis.
Sharp V threads called United States Standard threads. Used on brass pipe works. American National Threads replaces the Sharp V for general use. Unified thread is the standard agreed upon by the USA, Canada, Britain in 1948 and has replaced American National form. Square Thread are to transmission of power. 13.3 SCREW THREADS FORM
ACME Thread replaces the Square threads since it is difficult to manufacture. Whitworth thread (British standard) has been replaced by the Unified thread. Knuckle thread is used in electrical bulb and other electrical applications. Buttress Thread is designed to transmit power in one direction. 13.3 SCREW THREADS FORM (Continue)
Three method of representing thread on drawing. Schematic, use for smaller diameter, about 25mm (1 inch) Detailed, for diameter more than 25 mm (1 inch) Simplified, commonly used. Thread Symbol
Metric threads fit Two class of fit, one for general purpose, 6H for internal threads and 6g for external threads, therefore default class of fit is 6H/6g if not specified. Second class for closer fit, 6H for internal threads and 5g6g for external threads. 13.20 Metric and Unified Threads fit
A represents for external threads and B represents for internal threads. Number 1, 2 and 3 represents the class of fit. 2A/2B is general class and equivalent to 6H/6g 3A/3B for close fit. 1A/1B for Rapid assembly. Unified threads fit
Bolt: Through bolt, head on one end and passes through clearance holes and nut on other side.
Cap Screw: Similar to a bolt, has greater length, use without a nut. Other member has thread and acts as a nut.
Stud: A steel rod threaded on both ends. Screwed in one member and nut on other member.
MACHINE SCREW: is similar to the slotted head cap screws but in general is smaller. Can be used with or without nut. SET SCREW: is a screw with or without a head that is screwed through one member and whose special point is forced against another member to prevent relative motion between the two parts.
Clearance hole: A simple hole without thread used to insert a bolt. Tapped hole: A hole with internal thread. Read 13.24 page # 379 for more detail. There is clearance between clearance hole and the bolt or screw. For standard, see page # 379.
.75-10 UNC-2A x 2.50 HEXAGON CAP SCREW M8 X 1.25-40 HEX CAP SCR 5/8-11 UNC-2B SQURE NUT M8 X 1.25 HEX NUT