How do you tell if a coil of another brand will work on your detector?

I never know what makes one coil compatible with a particular detector. How do you know if a particular detector is configured for a concentric, DD, folded eight, or mono coil? Do you just try them on your machine if the connector is the correct one and see how they do? Can you harm the machine or coil by doing this? I have always bought the recommended coils for my machines but have so many coils now that I was wondering if it is safe to swap out coils on some of my machines rather than continually buying the same type coil for a different detector. There must be some technical info available to make informed choices other than reading what someone else says works best on their detector. Thanks for your help on this one guys. There I go showing my ignorance again....Stuart

A lot of questions there, without any specific details about machines etc.
Firstly, there are many different specifications in terms of inductances, resistances, connector pinouts, shielding arrangements, single-ended / centre-tapped, built-in capacitors or not, frequency they are nulled at, the list goes on. The result is that generally, coils are NOT compatible, unless they are specifically stated to be, for example across a range of similar machines from one manufacturer. Machines that work with concentric coils will generally work with DD types if they are electrically the same, and vice-versa, but sometimes things like Target ID / discrimination can be unreliable. There are a few inter-brand compatible coils, I've read that certain Whites 6.6KHz machines/coils work with other closely-related machines, maybe some Teknetics ones? And Some Bounty-Hunter/ Fisher/ Tek interchanges are possible.
Maybe if you posted a specific request you might get a yes/no reply. Alternatively, ask on Geotech1, they will likely know, or they will flame you, depending.

Hi search, if the ends will fit the detector, try the coil. DO NOT FORCE THE ENDS TOGETHER!!! but if they fit ok then put the detector in max mode and try the coil. It will not hurt the detector, if the coil is quit and stable it will work ok, maybe not the same VDI # but will still pick up targets. At least that is what i was told, i have done it and some work and some don,t. Good luck Flintstone

If you go to K Co coils you can do a basic cross check.