Abstract: A plastic clip to be tightened against a bolt comprises a plastic body having a base having a through hole to be penetrated vertically by the bolt, at least one upright post extending upright from the top of the base adjacent to the through hole, a cylindrical portion united to the outer end of the upright post and having a hole formed above and coaxial with the through hole in the base for receiving the bolt, and a flexible arm extending in a curved fashion from one side of the upright post between the base and the cylindrical portion to slightly project with respect to the outer shape of the cylindrical portion having a curved inner surface provided with a thread to be meshed with the male thread of the bolt, and a plastic operable cylinder fitted on the outer periphery of the cylindrical portion and lowered along the upright post to urge the flexible arm against the periphery of the bolt.