Question

You can use a _____ to test tread wear on your tires

Answer 1

I don't think you are asking the right website, but I'll try to help anyways.
Insert a penny upside down into the groove. If some of Lincoln's head is buried,
you have roughly 3/32s of an inch of remaining tread which is legal in most states.

However, a tire with that much wear isn't safe in the rain, where you need deep channels to carry away water to avoid hydroplaning.

New tires generally start out at a tread depth of 10 to 11/32s of an inch.