The tool chuck provides a standard connection between the various cutting tools and the machining center spindle. It works in a similar way to an adjustable drill chuck, just as a home repairman can replace a drill bit. The tool chuck provides a standard connection between the various cutting tools and the machining center spindle. It works in a similar way to an adjustable drill chuck, just as a home repairman can replace a drill bit. Machining center spindle holes and tool holders shanks and flanges are manufactured to standards that have evolved worldwide over the past 25 years. In general, these standards are well established and provide a solid, high degree of concentricity as long as both the spindle and the tool chuck meet the standards.