Abstract: An in-line arm assembly for releasably clamping a head-mounting fixture in a disk drive tester is disclosed. The in-line arm assembly includes a clamp housing, a movable gib, a removable head-mounting arm, a head-mounting fixture, and a means for moving the gib to activate and release the clamp. The clamp housing has a support surface and an inclined clamping surface. The gib is coupled to the clamp housing and has an inclined clamping surface. The head-mounting arm has a clamped member that engages the clamp with a bottom surface that is parallel to the support surface of the clamp housing and two opposing beveled surfaces that are parallel to the inclined clamping surfaces of the clamp housing and gib. The in-line arm assembly facilitates replacement of heads in the disk drive tester.