Metal detector search coils come in a variety of shapes and sizes from just a few inches across to a staggering 18in! Some are concentric (polo coils) and some are even “web” shaped. Several makes of detectors offer the ability to interchange from one type of coil to another.
Smaller coils tend to have better pinpointing ‘ abilities and are easier to use on rough ground or sites that are overgrown and where maneuverability is a problem.
Larger coils usually offer greater depth capabilities and can cover more ground in a shorter space of time. These coils quite often add considerable weight to a machine and are more suited to flatter ground surfaces.
Concentric coils put out a search field resembling an inverted cone. Size for size they usually go deeper and are often better when searching junk-infested sites. Double-D or wide scan coils, with their cylindrical search fields, normally provide better and faster ground coverage.
It is worth checking, before you make a purchase, that the type of detector you wish to buy can use interchangeable coils.