Thread Classifications
-There are three classes of thread fit;
Class 1 - A very loose tolerance thread class designed for applications involving easy assemble and disassembly of components.
Class 2 - “Standard” tolerance thread class used for general assembly.
Class 3 – High Accuracy thread class used for fine fits.
Designations for each class and the type of thread for Unified and Metric are listed below;
Unified Inch Standard
Metric
Class Loose
External Thread
External Thread
1A 2A 3A
8g 6g 4g
Standard
High Accuracy
Nomenclature: Example specifications for a threaded fastener are given below for both Unified Standard and Metric unit types;
Threads per Inch
Class of Fit(Tolerance Specification)
Type of Thread(A-External B-Internal)
1/2-12 UNC – 3 A
Classification
Major Diameter
UNC(Unified National Course) UNF(Unified National Fine) UNEF(Unified National Extra Fine)
(< 1/4" are numbered, #12 = 0.2160", #0 = 0.060")
Nominal Size(Diameter)
Fit Classification
M12 x 1.75 , 6g x 85
Metric
Pitch(MM)
Length(MM)
Made with FlippingBook - professional solution for displaying marketing and sales documents online