US 47875483 A description the spin fixture for measuring gyroscopic stability comprises a spherical shaped support body member 10 which fixedly holds a projectile 12 in a radially extending holding slot 14 projectile 12 is located in holding slot 14 so that its center of gravity 16 is operatively disposed so that it is coindicent with a radial axis of ball body member 10 body member 10 is supported by a lower female pole piece support members 18 18 39 and an upper female pole piece support members 20 20 39 having spherically contoured air bearing surfaces 22 and 24 respectively a plurality of air passages 26 are located in the lower support members 18 18 39 and a single air passageway 28 is located in the upper support members 20 20 39 passageways 26 and 28 carry high pressure air from air supply source 30 at a controlled rate by an air pressure regulator 32 to exit orifices 34 and 36 respectively orifices 34 and 36 supply clean dry pressurized air to the air bearing clearance space 38 located between the ball body member 10 and the spherically contoured air bearing surfaces 22 and 24 air passages 26 in.