NOVA 9090 Large Bowl Rest Bar is part of the modular NOVA Tool Rest System, a flexible system which allows you to mix and match your tool rest posts and supports to create the perfect tool rest for your needs. Requires one of NOVA Tools Rest Posts (additional purchase). This threaded Bar enables you to use different NOVA Tool rest Posts as needed. 8.5″ diameter curve is for turning the interior of bowls. The rest is radiused on the top and bottom edges for smooth movement of the chisels and it can be used in either orientation for greater versatility.