This is a Whiteside stile & rail bit, model 6009, ground for cutting matched frame joinery for cabinet doors. It measures 1/2″ shank, 1″ cutting length, 15-degree angle, and uses carbide cutting edges that resist heat and hold an edge far longer than plain steel.
Chuck it into a router table or handheld router to mill the matched stile-and-rail joints on frame-and-panel cabinet doors. The balanced bit runs true at speed, so cuts come out concentric and clean with minimal sanding afterward.
Whiteside Machine Company manufactures its router bits in Claxton, Georgia, and is consistently rated among the top-performing router bit makers in independent woodworking tests.
