An extruded plastic sheath product is provided to cover studded steel T-posts and hence give fence lines or sign posts and improved, even aesthetic appearances. The plastic sheath product is formed with a series of internal projections which abut against features of the internal T-post and hence prevent the sheath from spinning about the T-post. For the fence line filed of use, the plastic sheath product is further given an external spine which has formations or else studs formed in it to prevent fence wire strapped to the sheath from slipping. For the sign post field of use, the sheath is further provided with a series of coupling accessories in order to construct frames and the like. Such coupling accessories optionally include Ell's, Tee's, crosses, or y-shaped splitters. The shape and arrangement of the extruded tubular sheath is especially designed to accommodate certain shape anomalies which result from the extrusion process.