A fractional factorial experimental study was conducted to determine the effect of seal size on seal design. The seven factors studied were inside lip diameter (w/o spring), seal size, shaft-to-bore offset, spring position, contact width, flex section thickness, and material modulus. The fractional factorial experiment was designed so all interactions involving seal size were determinable. Leakage was measured as the response or dependent variable. The large seal (nominal 100 mm) differed from the small seal (nominal 50 mm) in three areas: (1) shaft-to-bore offset was not tolerated by the large seal, (2) the spring position was required to be closer to the contact line with the large seal, and (3) a higher material modulus was necessary with the larger seal.