Real pitch: The distance between 'V's after following a helical path around theĭiameter of the screw. (Not to be confused with the length of a thread) V-Shape: Pitch: The distance between 2 adjacent 'V' shapes. Length of engagement: Basic length of thread engagement that is defined by a combination Tolerances: Allowance: Fundamental deviation of the basic size, applies only to 1A and 2A externalĬlasses Major/Pitch/Minor diameters: The difference between the maximum and minimum diameters. Pitch diameter the external screw thread. Wire Diameters: Diameter of the wires used to measure the dimension close to the Of the same size to measure the dimension close to the pitch diameter of an external Threads Over wires distance: these are the maximum and minimum distances if using 3 wires (this is the most important dimension of a thread) Minor diameter: The maximum and minimum sizes of the smallest diameter of the screw Diameters: Major diameter: the maximum and minimum sizes of the outside diameter of a screw Pitch diameter: the Maximum and minimum sizes where the 1/2 Pitch intersects within It does not need to be specified forġ start threads. determines if it is an external or internal Can be a decimal number such as 4.5 threads example: 7/8-18 UNS 2A 2 starts 7/8: Basic outside diameter. Definition: This is the standard way of defining a screw thread. Have only 1 but a thread with multiple starts advance a greater distance for each of starts: This is the quantity of helical entries along the length of the screws. the tolerance classes 2A and 2B are within classes 1A and 1B. Most commonly used are the classes 2A andĢB. class 1A and 1B have the largest gap to classģA and 3B which have the smallest gap. The class tolerance determines the size of the gap between the pitch diameters of Screw thread (This series is not supported) Class tolerances: (If unsure, use class 2A for external or 2B for internal) Tolerance classes 1A, 2A and 3A apply to external thread Tolerance classes 1B, 2B and 3B apply to internal threads. Not supported) UNJ: high stress series thread with large rounded root on external UNR: standard series thread with rounded root. It also plays a role in determining the length of engagement. On aģ/4' diameter screw, 20 threads per inch is considered extra-fine: 3/4-20 UNEF. Threads per inch on a 1/4' diameter screw is considered coarse: 1/4-20 UNC. thread series designation: (UN, UNC, UNF, UNEF, UNS) The thread series is generally relative to the outside diameter of the screw. Number of thread that would fit along a one inch length. Shorter or longer than one inch, the size of the 'V' shape is still defined by the NOTE: If the length of the threaded portion of a screw or threaded hole is Size of the 'V' shape of the helical portion of a thread. TPI: (Threads per inch) The number of thread, or 'V's along a one inch length which in turns, defines the NOTE: The size of the hexagon of a bolt or nut has no relevance when definingĪ thread size. The biggest externalĭiameter of a Screw or the biggest internal diameter of a threaded hole.

Outside diameter: This is the biggest diameter of the helical portion of a thread. It will work with threaded holes or shafts made by other manufacturers that follow Making a thread that follow these specifications will ensure that Imperial UN: (Imperial Unified National thread form) A standard that describes the shape of an internal or external thread using imperial Of the ANSI/ASME B1.1-1989 specification. The algorithms used for this calculator are based on the 'my' best interpretation Inch, series designation and class tolerances. Glossary Thread calculator: All calculated results are based on Basic outside diameter, number of threads per

Decimal drill chart