Project running you in circles? Trace perfect arcs or circles in an instant with a ballpoint pen, an awl or a nail, and a short length of plumber’s chain (60 cents a foot at home centers). The pen pokes through the chain’s smaller links just enough to create an exact radius when you keep the chain taut while tracing. As a bonus, each link provides a 1/2-in. increase or decrease in radius for quick adjustments without measuring. Thanks to reader Bill Waite for hooking us up to a well-rounded tip.