Model: T140, T180, 864, T190, T200, T250, T300, T320, T550, T590, T630, T650, T750, T770. △ Top Roller. Part Type: Bottom Roller. Yield strength σ0.2 (MPa):≥310. △ Sprocket. Roller, 45# carbon steel or 40Cr, quenched HRC25-30, surface quenched HRC52-58, hardened to a depth of 2-3mm.