Cholla is a Cactus found in the Southwest. What you have is the skeleton of the Cactus. You will have to cast a resin blank around it in order to turn it safely without falling apart. You can use Mineral or Stone fillers, or add color to your resin, in order to fill the holes in the Cholla. Try to keep the Cholla centered in the blank when you cast it in order to keep an even pattern when turned. When you drill your tube holes, go from center to center on the ends of the Cholla, not center to center on your blank !! If the blanks came from PSI, they should be pre drilled for a pen already. Look for a kit with that size tubes. Makes a stunning looking pen. Good luck !!! Jim S