The glass fibre pencil is used in the modelling world to perform precision sanding work, to realize stressed panels and simulating the dents in sheets metal in an easy and controllable way. To eliminate glue spills before the painting process and thus avoid unwanted effects, for this and many other uses.
The fibre tip that can be replaced by a new one when worn out.
*Recommendable: Work in glasses and gloves, and thoroughly clean the workplace with vacuum cleaner after finishing the job. The small pieces of glass fibre that crumble during the sanding process, can be really dangerous.