PRO-4 with Corner Radius - Series 191 Series 191 Vibration Reducing End Mill with Corner Radius. The patented PRO-4 by PROMAX. View Speeds & Feeds page. Features: Eliminates Chatter & Vibration While Delivering an Excellent Finish Relieves cutting pressure against the tools with OD Chip Breakers Easy & Inexpensive to Regrind Available in Multiple Raidius sizes Standard with Advanced AlTiN Coating (Part Number ends in 4) Standard with Advanced nACRo® Coating (Part Number ends in 5)