filetage unifié à pas fin UNF

CONT: Norme BS 1580 : 1953 ""Unified Screw Threads"". Il s'agit des filetages cylindriques de mécanique générale, au profil ISO, mais avec les cotes en pouces. Depuis 1949, le Royaume-Uni, le Canada et les États-Unis se sont mis d'accord sur ces filetages et leur désignation : ""UNC"" pour ""Unified coarse thread"" (gros pas). ""UNF"" pour ""Unified fine thread"" (pas fin). ""UNEF"" pour ""Unified extra-fine thread"" (pas extra-fin). ""UN"" pour ""Unified constant pitch"" (pas constant). Ces filetages figurent [...] d'une manière plus complète dans la norme américaine ASA B1.1-1960 qui concerne les filetages unifiés.

CONT: Unified and American National screw thread standards for screws, bolts, nuts, and other threaded parts consist of six series of threads and a selection of special threads that cover nonstandard combinations of diameter and pitch. In general, the unified screw threads are limited to three series: coarse (UNC), fine (UNF), and extrafine (UNEF). A 1/4-inch.-diameter thread in the UNC series has 20 threads/in., while in the UNF series it has 28. ... The fine thread series (UNF and NF) is recommended for general use in the automotive and air craft fields for threads subject to strong vibration. In general, a fine thread should be used only where close adjustment, extra strength, or increased resistance to loosening is a factor.
CONT: Threads are designated by standardized notes. Under the unified system, threads are specified by giving in order the nominal diameter, number of threads per inch, the initial letters such as UNC or UNF that identify the series, and class of thread (1A, 2A, and 3A or 1B, 2B, and 3B). Threads are considered to be right-hand and single unless otherwise noted; therefore the specification for a left-hand thread must have the letters LH included.
CONT: [Example of a thread identification by standardized symbols]: 1/2-13UNC-2ALH.