UNC – Unified National Coarse
UNF – Unified National Fine
UNEF – Unified National Extra Fine
UNS – Unified National Special
UNR – Unified National Round (round root)
ISO – International Standards Organization (metric) 

Two major Unified thread series are in use: UN and UNR. For the UN series, you specify C
(coarse), F (fine), or EF (extra fine), as required. For the UNR series, the root radius must also be specified.
The UNR series screws are better for fatigue because the root radius reduces stress concentrations. The
basic thread geometry for ISO and Unified threads is n below.
Thread Standards and Definitions
Pitch (p) – The distance between adjacent thread forms measured parallel to the thread axis.
Lead (L) – The distance the nut moves parallel to the screw axis when the nut is given one turn.
TPI (n) – The number of Threads Per Inch, related to the pitch by p = 1/n.
Root (minor) Diameter – Smallest diameter of screw - dr.
Major Diameter – Largest diameter of screw - dc (sometimes designated as d).
Mean (pitch) Diameter – Average diameter of screw - dm (sometimes designated as dp).
Lead Angle (λ) – The angle defining the inclination of the thread (see figure below).
Helix Angle (ψ) – The angle between the thread axis and the lead angle (ψ + λ = 90o).

   GSG螺紋量規(guī)制造廠是全美的非標(biāo)量規(guī)制造商，提供全系列的非標(biāo)量規(guī)設(shè)計(jì)解決方案，可以根據(jù)圖紙，根據(jù)參數(shù)、根據(jù)客戶的要求設(shè)計(jì)、制造量規(guī)，深受歐美企業(yè)的，蘇州斯文克精密測(cè)量設(shè)備有限公司作為美國(guó)GSG量規(guī)的中國(guó)區(qū)代理商，銷售各類量規(guī)，部分常用量規(guī)備有庫(kù)存，期待您的咨詢。