Method 1 – Drop to 4khz
Check it by using a program that uses the 4kHz frequency. You can either go into the menu and just drop the frequency, or you can create a duplicate program adjacent to the program you’re using, and flip over to it. For me, the screw caps usually either ring up around 83-85, or sometimes in the low 90s (that’s using 12 kHz). When you switch to using the 4kHz frequency, if it is a legitimate target, you’ll see the target ID DROP. If it is a bottle cap, you’ll see a target ID HIGHER than what you were seeing before you switched. On some wine screw caps (which ring in lower for me, usually in the upper 70s), sometimes I’ll get virtually the same reading (not higher) when switching to 4 kHz, but that still tells you the same thing because a good target will show a lower ID in 4 kHz than in 12 kHz (or 8 kHz). While air tests aren’t valid for many uses, you can use an air test to see this target ID behavior in action and see it for yourself.