Horizontal Milling Attachment R8 w/ Support (50° dovetail) & Arbor. Horizontal Milling Attachment with Arbor – R8 Fits Bridgeport-style milling machines with a 3 3/8 (8586mm) quill diameter and R8 spindle taper Converts a vertical mill into a horizontal mill Note: Maximum allowed speed with right angle attachment is 2000 rpm. Spindle runout is ± 20 micron (0.00078) The dovetail angle on milling arbor support is 50°. (Note: 50° is more common than 55°, we have both available) Complete Set Includes. 7/16-20 bolt with 1/2 hex head. If you have any questions regarding this item, please let us know we’ll be happy to help. If You have any questions regarding this item, please let us know we’ll be happy to help.