The following was taken from a chart in INAV (in the 60's, I think...)
Diameter
Torque (in./oz.)
Constant
.010
.31
6.20
.012
.54
2.97
.014
.86
1.60
.015
1.06
1.21
.016
1.28
.939
.018
1.83
.594
.020
2.51
.383
This data may be used with the following formula:
length = 6.28/tK
Where:
length = length of the torque wire in inches
t = Torque desired for one revolution of the dial
K = Constant from the above table
Example:
Desired torque with .015 wire of .6 in./oz.
length = 6.28 / (.6 * 1.21)
length = 8.64"