ASME B1.10M specifies the thread form. seties tolerance, and designation for the Unified Miniature Screw Threads. The series covers a diameter range of 0.30 mm to 1,40 mm. extending the metric M-Proflie and unified thread series that begin at 1.6 mm.
1.2 Unifled MIniature Screw Thread Standards
The fourteen sizes published in this Standard were endorsed by the AmerIcan-British-Canadian conference of Aprii 1955 as the basis of the unified standard among inch-using countries, and to correspond with the range of eizs in the lx). The sizes are shown in Table 1. In interest of tandardjzation and where design pernuts. selection of size should be confined to those indicated in bold type in Table 1. For more restrictive conditions, those sizes indicated in regular type in Table 1 may be used.
1.3 DesignatIon
Unified Miniature Thread sizes of this series shall be designated on engineering drawings. in specifications. and on tools and gages (space permitting) by their nomi nal diameter in hundredths of a millimeter followed by the symbol UNM (e.g.. 0.80 LJNM).
On internal threads, the full limits of minor diameter, as given in Table 2,. shaLl normally be considered applica. ble. Where this is not permissible, the designation shall be supplemented by the minor diameter limite.
1.4 Reference Document&
The following is a list of pubLications referenced in this Standard.
ASME B).?, Nomendature, Definitions, and Latter Symbols for Screw Threads
ASME B1.30M. Screw Threads—Standard Practice for Calculating and Rounding Dimensions
Publisher The American Society of Mechanical Engineers (ASME International), Three Park Avrnue, New York. NY 10016-5990; Order Department: 22 Law Drivc, Box 2300, FaIrfield, NJ 07007-2300
1.5 AcceptabilIty
Add thonal recommended methods for determining the acceptability of miniature screw threads will be included as further experience with this thread standard is reported. Until such time, agreements must be readied between purchaser and vendor regarding the basis for determining acceptance, since practices are likely to difler considerabl particularly for external threads. Where a free choice is possible, the procedures given below, which are being used with coosderable success by some producers. are suggested
1.5.1 External Threads. The major diameter of the external thread Is measured by either contact gaging, optical proectlcn. or laser inspection equipment AU other dimensions, such as pitch diameter, lead, thread form, and minor diameter may be inspected by optical projection methods, with a magnification of W0Xrecom- mended. A suggested chart for this method is shown in Appendix A The thread plug gages and the tap are inspected in a similar manner to externally threaded paz1. Contact gaging, such as the use of G0 and NOT GO’ ring gages, measuring wires, and set plug gages may be used for sizes 0.70 UNM and above.
1.5.2 Internal Threeds. The minor diameter of the internal thxrad is gaged with ‘GO and N(YT GCY plain cylindrical plug gages All other elements are checked only for assemble-ability limits by means of a G0 thread plug gage, takmg extreme care not to damage the thread. For the minimum material limits of the internal threads, the accuracy and performance of the tap is relied upon This impLies that the major and pitch diameters of the tap do not exceed the maximum internal thread Limits for these elements, and disregards over cutting. which is rarely incurred because of the flexibility of these small tape and the manner in which they are generally fluted
It is recommended that the minor diameter of the internal thread be gaged with one insertion of the NOT GO’ plain cylindrical plug gage first.