Series 11U is a single conical helical spring unbalanced seal with 'O' ring as secondary sealing member. Various seal face materials and elastomers can be offered for wide service application. As the torque transmission is done by conical helical spring, these seals are dependent of the direction of rotation. Direction of rotation is seen from the drive end of the shaft. Clockwise rotating shaft requires right handed spring and anti-clockwise rotating shaft requires left-handed spring. For easier fitting the conical helical spring should be pushed on the shaft with a twisting motion in the sense of the spring winding. This movement enlarges the diameter of the spring, enabling easy fitment.