Crain 310 double-needle dividers have a rounded radius arm for adjusting the distance between the legs, and a large wing nut for holding the legs in position. The legs span from ½" to 6" apart. The rounded arm provides smooth adjustment and solid hold. The needles on both legs are replaceable (No. 311). Comes with two needles in the tool, and two separate replacement needles. Crain 310 Dividers replacement needles are held in the legs by a precision press fit.