Stainless steel type 303, 3.750 in. Porm 0.093 in. Lg, 0.750 in. Min, 0.775 in. Max thk, pole piece stainless steel type 416, internal portion potted w/epoxy resin, minus 100 degrees f to plus 225 degrees f temp range, 5/8-18 unf-2a thd, locknut, dc resistance 1190 to 1450 ohms, inductance 400 to 600 mh measured w/6v rms at 1 kc