An electrical insulator for use with a rail fastening clip comprises a contact member providing on one side a substantially flat rail contact surface for contacting a foot of a rail and on the opposing side a clip contact surface for contacting a rail bearing surface of a bearing portion of the clip, the insulator also having retaining means for retaining the insulator on the clip in such a way as to allow rotation of the insulator about a longitudinal axis of the bearing portion of the clip. The insulator has stop portions for limiting such rotation about the longitudinal axis of the bearing portion of the clip to a desired extent. The clip contact surface of the insulator is convex, in a vertical plane which is perpendicular to the longitudinal axis of the bearing portion of the clip, such that, when the insulator is attached to a clip having a flat rail bearing surface, a contact region between the flat rail bearing surface of the clip and the clip contact surface of the insulator is linear. The insulator is rockable about the linear contact region within the extent defined by the stop portions such that, when the rail contact surface of the insulator contacts the surface of a rail foot, the angle of the rail contact surface can conform to the angle of the rail foot surface. A rail fastening clip, suitable for use with the insulator and of the kind driven onto a rail in a direction which is parallel to a longitudinal axis of the rail, has a bearing portion having a flat rail bearing surface, wherein a detent, extending laterally with respect to the longitudinal axis of the bearing portion, is formed in the flat rail bearing surface, at a location spaced from a free end of the bearing portion of the clip, for engaging a corresponding abutment surface of the insulator to be retained on the rail bearing portion of the clip.