If you know the brand of your tank look for the manufacturer here, to find the right replacement coils.
Aspire Brand Replacement Coils
Eleaf brand replacement coils
Freemax Starre Tank Coils
Innokin iClear 16b coils
Joyetech replacement coils
Kangertech Replacement Coils
Sense coils mostly for the Herakles line of tanks.
SMOK makes a wide variety of tanks. All of these coils are Geniune SMOK brand coils
Tobeco brand replacement coils
Vape Only replacement coils made by aspire for Vape Only tanks
Vaporesso Target & Target Pro Coils
Wismec Elabo Tank Coils