Fisher 4" Search Coil - Fits F2 and F4 The Fisher 4" search coil delivers great performance in tight, hard-to-reach spots; highly mineralized soils; and high-trash areas. Plug-in style search coils fit older model Fisher detectors with serial numbers earlier than (less than) 0610XXXXXX. Compatible with the Fisher F2 and F4 metal detectors All Fisher search coils are 100% waterproof