These 25 mL PYREX® glass volumetric pipets were designed primarily for schools and laboratories where the Class A tolerance of No. 7100 is not required. They are constructed to the same wall thickness and length as our No. 7100, but have larger tip openings for faster delivery. It is primarily due to this faster delivery that accuracy tolerances are twice those specified for Class A volumetric ware. Reference: ASTM E-969.