A disk drive includes a fastening structure to secure a shaft between parallel walls which will secure and locate the shaft without inducing a distortion of the walls. One end of the shaft is secured to the adjacent wall and the other end of the shaft is secured through a wall opening using an annular slug 43 and a deformable washer 45 which is compressed by a bolt 41 attached axially to the shaft end to cause the deformed washer to engage the surfaces defining the wall opening 32. The uniform axisymmetric expansion of the washer does not affect the position of the shaft and the radial force secures the shaft end without influencing the structure of the casting.