I came to this question few years ago and had done some further study on them.......We need to use the Appendix C - d2 table for K constants calculation.
K1 - Used for Repeatability, Equipment Variation (EV) calculation
Find the d2 from Appendix C - d2 table,
focus on the subgroup size(m) for
number of trials we used in GR&R study, number of subgroups (g) for
parts x number of operators we used in GR&R study. If the parts x number of operator greater then 20, find the d2 at the bottom of the table.
K1 = 1/d2
K2 - Used for Reproducibility, Appraiser Variation (AV) calculation
Find the d2 from Appendix C - d2 table,
focus on the subgroup size(m) for
number of operators we used in GR&R study, number of subgroups (g) is set as 1 as there is only one range calculation in this study.
K2 = 1/d2
K3 - Used for Part Variation (PV) calculation
Find the d2 from Appendix C - d2 table,
focus on the subgroup size(m) for
number of samples we used in GR&R study, number of subgroups (g) is set as 1 as there is only one range calculation in this study.
K3 = 1/d2
AIAG MSA guideline used formula K = 1/d2, all the sigma (EV, AV and PV) calculated used the original formula with K value replaced and %PT Ratio = (100x 5.15 x sigma R&R)/product specification.
Larry B. Barrentine used formula K = 5.15/d2, all the sigma (EV, AV and PV) calculated used the original formula with K value replaced
BUT divided by 5.15 backand %PT Ratio = (100 x 5.15 x sigma R&R)/product specification.
Noted: We do not use the factor 5.15 or 6 in GR&R% calculation (compare to process variation), it is only apply in PT Ratio calculation (compare to product specification)