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Wednesday, October 7, 2015

Pre-Plate pitch diameters, major diameters, and minor diameters of thread rings, thread plugs, and plug gauges.

The rules for determining Pre-Plate pitch diameters, major diameters, and minor diameters of thread rings, thread plugs, and plug  gauges are as follows:


To determine Pre-Plating dimensions for external threaded parts: 

For external threads subtract the max plating thickness from the high limit Pitch Diameter, and then subtract the minimum plating from the low limit Pitch Diameter  

For the minor and major diameters reduce the maximum diameters by half the maximum plating and reduce minimum diameter by half the minimum plating.   


To determine Pre-Plating dimensions for internal threaded parts: 

For internal threads add the max plating thickness to the low limit of the Pitch Diameter, and then add the minimum plating thickness to the high limit of the Pitch Diameter.  For minor and major diameters increase the minimum minor diameters by half the maximum plating and increase the maximum minor diameter by half the minimum plating. 


To determine Pre-Plating dimensions for thread ring gauges: 

For thread ring gauges subtract the max plating thickness from the Pitch Diameter of the Go thread ring gauge. Then subtract the minimum plating from the Pitch Diameter of the No-Go thread ring gauge. For the minor diameter reduce the Go ring minor diameter by half the maximum plating and reduce the No Go ring minor diameter by half the minimum plating. 


To determine pre plating dimensions for thread plug gages: 

For thread plug gauges add the max plating thickness to the Pitch Diameter of the Go thread plug gauge.  Add the minimum plating thickness to the Pitch Diameter of the No-Go thread plug gauge. Increase the major diameter of the Go thread plug by half the maximum plating and increase the No Go thread plug major diameter by half the minimum plating. 


Example for Thread Plug Gage:

Plating of .0002” - .0003” allowance per side multiple x 4
.0003 x 4 = .0012” Max
.0002 x 4 = .0008” Min


½ - 20 UNF 2B Pre-Plate

Basic standard Go Pitch Diameter = .4675” + .0012” = .4687” Go  Pre-Plate Pitch diameter.
Basic standard No Go Pitch Diameter = .4731” + .0008” = .4739” No Go Pre-Plate Pitch Diameter.
Basic standard Go Major Diameter = .5000” + .0006” = .5006” Go Pre-Plate Major Diameter.
Basic standard No Go Major Diameter = .4948” + .0004” = .4952” No Go Pre-Plate Major Diameter.


Example for Thread Ring gages:

Plating of .0002” - .0003” allowance per side multiple x 4

.0003 x 4 = .0012” Max
.0002 x 4 = .0008” Min
.0003 x 4 = .0012” Max
.0002 x 4 = .0008” Min


½ - 20 UNF 2A Pre-Plate

Basic standard Go Pitch Diameter = .4662” - .0012” = .4650” Go Pre-Plate Pitch Diameter
Basic standard No Go Pitch Diameter = .4619” - .0008” = .4611” No Go Pre-Plate Pitch Diameter
Basic standard Go Minor Diameter = .4446” - .0006” = .4440” Go  Pre Plate Minor Diameter.
Basic standard No Go Minor Diameter = .4511” - .0004” = .4507” No Go Pre-Plate Minor Diameter.

If no minimum and maximum plating thickness is given, then the given plating thickness is considered nominal or minimum plus 50% to determine maximum plating.