Bob On page 9 of the May 1969 "RTTY Journal" article by Ron Guentzler, he states "The inductance of pulling-type magnets is about 4H; the inductance of parallel-connected holding-type magnets is about 2 H". One would assume that this latter value would be close for Model 28 selector magnets. Hope this helps. Tim Swarthout, WA5QEG