Guides Internal Cannula to injection site. Consists of a threaded cylindrical plastic pedestal molded around a piece of stainless-steel tubing that extends below the pedestal. The pedestal is secured with cranioplasty cement and mounting screws or cyanoacrylate gel. The 2mm pedestal Guide Cannula is too short to use a regular Dummy Cannula. A Dacron mesh option is also available if needed as an attachment to the guide pedestal. Pedestal Diameter. 3.5 mm (.138").