cap 40 has a bore 42 which terminates in a flat interior surface 44 the bore 42 receives the anti friction washer 50 with elastomeric washer 50 engagable with the interior surface 44 of the cap 40 the retaining cap 40 is provided to hold the assemblage together in the bore 30 as illustrated in fig1 the cap 40 has a flat annular face 43 at the open end the second high friction elastomeric washer 50 has flat faces 51 and 53 an outer diameter 52 and an inner bore 54 which is larger than the outer diameter 10 of the lead screw 4 a circular opening 55 is formed at the left hand face of the cap 40 and is of larger diameter than the outside diameter of the lead screw 4 the bearing 8 which is pressed by the washer 50 in turn presses against the anti friction washer 34 and the washer is pressed against the surface 32 the high friction washers 34 and 50 prevent shifting of the carbon filled bearing 8 preventing mechanically induced movement but at the same time permitting thermal expansion or contraction of the bearing 8 uniformly in the radial direction heat is generated at the contacting surface 10 of the lead screw 4 and the inner diameter 9 of the bearing 8 since their coefficients of expansion are essentially the same as the lead screw 4 grows radially the inner diameter 9 of the bearing 8 grows an equal amount maintaining the elements in contact at all times thus.