XHT BLADES Extreme Hardness Toughness Replacement XHT Lawnmower blade. XHT(Xtreme Hardness & Toughness) blades are 25-40% harder than standard lawnmower blades. Benefits of the HXT blade are sharper and longer lasting cutting edges. More resistance to bending. Tighter tolerances in the aftermarket vs. OEM. XHT blades also offer greater impact toughness. By the way they are made in the USA This sale is for 3 replacement XHT blades. EXMARK 1-303146 1-303527 1-633484 1-633485 103-1578-S 103-2518 13-5218-S 103-6337-S 103-6582 103-6582-S (3) needed for 52" Cuts. Center Hole: 5/8" Width: 2.5" Thickness: .197" Length: 17-29/32" Medium lift mulching blades Â· Disclaimer: We list model numbers and part numbers for references only. At times the same model may take different parts based on serial number breaks or manufacturers specifications. We list all the specifications on the part (size, width, length, thickness, etc.) and YOU must know what is needed on YOUR application. We canÂt possibly make it more known as to what you are receiving when you purchase.