Abstract: A fastening system for attaching a flexible sheet or cover such as a polyethylene film sheet to a structure comprising a rigid channel which extends along the line where the sheet is to be fastened and attached to the structure, and a plastic lock strip that inserts into the channel and will retain the film relative to the channel. The plastic lock strip includes a spring means that will continuously urge the lock strip into a detent holding position with respect to the channel to insure that this film is held securely even under situations where there is little tension in the sheet or film. The features further include a pinching type detent that increases the holding force for any given tension in the plastic sheet.