Circle Keychain with Circumference Formula

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This round engraved acrylic keychain features the formula for figuring out the circumference of a circle (2 pi r). The "r" radius is marked on the keychain. A fun accessory for a f avorite math teacher or geometry lover! I used an extra thick acrylic (thicker than used for jewelry) to make it more durable. The acrylic makes this keychain very lightweight. The transparent options will shine in the sun like glass. Acrylic can scratch and break if it comes into contact with hard or sharp elements, so treat it with care. The keychain is finished with a strong stainless steel key ring. This costs a little more than the more common, cheaper nickel-plated key rings, but it has the advantage of being rust resistant when it gets wet. Colors: Choose your color at checkoutSize: 2.5"This is the full size of the keychain from the top of the key ring to the bottom of the charm. Show more