Silver Tone Medium Pi Clip On Charm. Silver Tone Medium Pi is approx. 0.59 x 0.47 x 0.08 (HxWxD) including loop. The irrational number Pi is a mathematical constant, the ratio of a circle's circumference to its diameter, approximately 3.14. It has been represented by the Greek letter since the mid-18th century. Clip On Charms may be added to your favorite jewelry. Silver Tone Swivel Lobster Claw Clasp is approx. 13 x 7 mm.Also available as a necklace, and bracelet. PLEASE NOTE: Our products are lead safe, but are not intended for children 14 years and younger.