a coupling device for adjusting the contact pressure between a balance weight and a rotative lead screw in an analytical balance . the weight is threaded upon the lead screw , and is advanced along a balance beam as the lead screw is caused to turn . the balance weight is substantially supported in rolling contact with the frame of the balance beam , and therefore , adds very little contact pressure to the lead screw connection . a leaf spring operatively connected between the balance weight and the lead screw adjusts the force exerted between the lead screw and the balance weight to a predetermined level .