It is possible to use standard 60 degree thread measuring wires to calibrate 55 degree British thread plug gages and external product. Thread Check often receives inquiries for special thread measuring wires to calibrate Whitworth/British 55 degree threads. Although Thread Check Inc. can certainly supply these special thread measuring wires, the cost is higher and the lead time to manufacture is typically 4 weeks or more. The best solution is to select a standard 60 degree thread measuring wire which is close to the 55 degree thread measuring wire diameter and simply adjust the constant value. This alternative set of thread measuring wires with an adjusted constant for the 55 degree thread angle will achieve the same exact results. The same method can be applied to 29 degree Acme and 45/7 degree buttress threads. All “Best Size” thread measuring wires have a maximum and minimum wire diameter that may be used to measure pitch diameter. Maximum and minimum thread measuring wires should be used which are safely within the limiting dimensions given by the formulas below.  

Include Thread Angle	Max.	Best	Min.
60°	1.010362p	.57735p	.505182p
55°	.82573p	.563692p	.50568p
29° Acme	.650013p	.51645p	.487263p

P=pitch  n=TPI   P=1/n The wide range of standard wire diameters in stock found within the 60 degree inch and metric sizes and the 29 degree acme sizes makes it possible to find a wire diameter very close to a required British or special size. The measurement of pitch diameter is least effected by an error in the included angle of the thread by a wire diameter which is closest to the calculated best size wire. Related topics regarding thread measuring wires: https://www.threadcheck.com/technical-documents/tc-thread-measuring-formulas.pdf https://www.threadcheck.com/the-three-wire-method-of-measuring-pitch-diameter/technicalinfo/ https://www.threadcheck.com/thread-measuring-wires-the-foundation-of-proper-thread-calibration/technicalinfo/ https://www.threadcheck.com/3-wire-thread-measuring-systems-info/technicalinfo/ https://www.threadcheck.com/calibrating-thread-measuring-wires/technicalinfo/ Thread Check’s expert sales engineers can assist our customers with selecting the correct wire size and calculating the new constant value to ensure accurate measurements. Thread Check Inc 900 Marconi Ave Ronkonkoma, New York 11779 Tel: 800 767 7633 info@threadcheck.com www.threadcheck.com