Those are the ones! I'da never thought anyone else would know what I was talking about if I referred to them as "cow stomach" magnets.
I knew what you meant.
Big oblong magnets that look like a wormer-pill.
You grease 'em up with lard, poke it in the pill-gun, grab the cow by the nostrils and lift her head up and back, slide the business end of the pill-gun in the corner of her mouth, over the tongue, and as far down her throat as it will go, then push the plunger, popping the pill out.
Then you hold her head up and massage her throat until she swallows.
Turn her out of the head-gate and twenty foot away, she spits out the pill.
Any of this sound familiar ??