Hope Woodturning's 10mm hook tool. This hook tool is 30% smaller size to the 12mm hook and designed for undercutting and hollow forms about 200mm deep with a small handle fitted.
 
Designed to get into hollow forms for under cutting and cleaning up. The HSS 10mm tip is made from cryo HSS and keeps its edge for a long time. The tool comes with a torx key and round bar tip holder for sharpening the tip.  Simply screw the tip on the holder and then sharpen in a battery drill on a diamond file. Avoid a grinder as this would shorten its life by grinding too much away.
 
The end is machined to 10mm. This will fit into a quick release or grub screw handle of that size, or it will fit into the hollowing rig with the 10mm collet.