XHT 17-3/8" Mower Blade - B1CC1419 XHT (Xtreme Hardness & Toughness) blades feature a unique steel that incorporates boron, carbon, manganese, and other materials that ensure its strength. The blades are heat treated with the patented and independently tested Marbain heat-treating process. This process makes the blades 25% - 40% harder than standard lawnmower blades, making them the longest-lasting, safest, and most impact resistant lawnmower blades on the market. Center Hole: 3/4" Length: 17.350" Replaces: Ariens / Gravely: 3971900 Thickness: .187" Type: High Lift - Notched Width: 2.250" Crossed From: 03746500 ARIENS / GRAVELY 03971900 ARIENS / GRAVELY 13177 ROTARY 3971900 ARIENS / GRAVELY This is an aftermarket product, not an OEM. Thanks for looking!