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ThreadSpecs3 ™


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Buttress Threads

This software supports three profiles in which the flank angles are 45° and 7° : External, but not internal, threads in all three profiles have an allowance.

"American" buttress threads have a thread height that is .6 times the pitch. Buttress threads have two tolerance classes each for external and internal : 2A,3A and 2B,3B, roughly analogous to the UN classes.
Reference : For product and gage threads, see ANSI B1.9-1973, except for Setting Rings. This software calculates Setting Rings using the ANSI/ASME B1.2-1983 standard.

British buttress threads have a thread height that is .4 times the pitch. British buttress threads have three tolerance classes : Free, Medium and Close, in order of smaller tolerances.
Reference : For product threads and working plug and ring gages, see BSI 1657:1950. This software calculates setting plug and ring dimensions using the same rules as for the "American" buttress threads.

Metric MJB buttress threads, where the height is .667982 times the pitch. The standard tolerance classes for MJB threads are 4d for external and 4H for internal. As with 60 degree metric threads, the "4" represents the tolerance grade and the letter represents the position that specifies the allowance. When more than one start is specified, the external tolerance position changes; the tolerance classes for 2 or more starts are 4c (2 starts), 4b (3 starts) and 4a (4 starts).
Reference : For product threads, see SAE MA 1696 2001-10. For gages, this software calculates gage dimensions the same as for "American" buttress threads.


Tips on using this software : MJB

Specify a number of starts, so that the software will determine the external tolerance class and fill in the remaining dimensions.

The Taylor Principle requires that the minor diameter of the NOT GO working ring not be less than the minor diameter of the GO ring. The B1.9 standard for gages, applied to MJB, tends to violate this rule. Consequently, in such a case, this software will display the minimum minor diameter of the NOT GO ring to be the maximum minor diameter of the GO ring. This will be flagged by a yellow background.


Gages

Working Thread Rings are used to gage external product threads. The "GO" ring should assemble with the product it is gaging, whereas the "NOT GO" ring should not. Generally, the minimum major diameter is specified, without a tolerance.

Working Thread Plugs are used to gage internal product threads. The "GO" plug should assemble with the product it is gaging, whereas the "NOT GO" plug should not. Generally, the maximum minor diameter is specified, without a tolerance.

Setting Rings are used to set indicating gages for internal product threads. GO rings are used to set gages to the maximum material size, NOT GO for the minimum material size. Generally, the minimum major diameter is specified, without a tolerance.

Setting Plugs are used to set indicating gages for external product threads, in addition to adjustable working ring gages. GO plugs are used to set gages to the maximum material size, NOT GO for the minimum material size. Generally, the maximum minor diameter is specified, without a tolerance.


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