Descriptions:This flex shank installer drill bit guide tool is really a must have for any electrician wallfishing any lines,it makes everything faster and more efficient. Also works great for the DIYer and professional too.Our practical brass stopper is a helper for you to prevent drill bit from drilling though sides off wall cavities. And also can be used as a stop so you don't accidentally pierce any ducts etc.This simple and creative flex shank installer drill bit guide kit is designed to keep the drill shank straight while working, making it easy to install wires or cables in hard-to-reach places.The helpful drill bit guide tool is very easy to use, just need to insert the flex shank bit into the wood bumper ball, and use the L-wrench to tighten the plug to keep the ball in the top position, then it works.Specification:Material: Wood + Stainless Steel + BrassSize InforLarge Bumper Ball Diameter: 2.36"/6 cmSmall Bumper Ball Diameter: 1.8"/4.5 cmBoth Ball's hole diameter are 0.23", and are fit for 3/16" shank.Package: 1 x Large Wooden Ball1 x Small Wooden BalL1 x L-wrench 1 x Brass Stopper