...the only coils that will work on the Garrett XL500 PI...are the Garrett 8.0 and 13.0 inch coils ...these are specifically made for their Pulse Unit....they are both open loop and look like the old BFO Coils....there are no other coils that are compatible ...although I did buy a 10 inch Custom Coil for it back in the late 1980's......not sure what is still available from Garrett since this detector was probably discontinued at least 10 years ago...most of my extra accessories for this detector I have bought off FeeBay......HH...........Joe