Three Wire Thread Measuring

Textbook Formula

Maximum wire size

Ideal wire size

Minimum Wire Size

Measurement formula

.900 / N

.57735 / N

.560/N

(D + 3W) 1.5155,N

 

Example: To calculate wire sizes and measurement for a 7/16 - 14 thread.

Maximum wire size

Ideal wire size

Minimum wire size

.900/14 = .064

.57735/14 = .041

.560/14 = .040

Note that in the following formula I am using a .045 wire not the .041 Ideal wire size. This is because there is not .041 wire in the standard set. Therefore use the next size larger wire in this case .045

 

Measurement formula

M = D + 3W - 1.5155/N = .4375 + 3(.045) - 1.5155/14

M = .4375 + .135 - .1085M

M = .464

M = Measurement over the wires

D = Major (outside) diameter of thread

W = Selected wire size

N = Number of threads per inch

A set of wires for this method consists of the following wire sizes.

.018, .024, .029, .032, .040, .045, .055, .063, .072, .081, .092, .108, .120, .127, .143, .185

Be aware that even though your formulas might give you another number you can only use a wire size FOR WHICH YOU HAVE A WIRE!!