In reply to Madhavbc.

It's a Pilot Hi-Tec C Coleto multipen. They have a handful of bodies/colors available to hold from 2-5 gel ink pen/mechanical pencil/eraser inserts with 0.3, 0.4, 0.5mm tips. This one in particular is their silver one for about US$10. I've got about 10 different pen bodies around the house/office with several dozen pen color refills always on hand.