Device for increasing the attraction force of fixing screws in soft material. The priority of the german patent application f35947 v/37b is claimed (Machine-translation by Google Translate, not legally binding)

摘要

Device for increasing the force of attraction of fastening screws in soft material, such as corrugated sheets of fibrous or similar material, applied especially in the fixing of corrugated asbestos sheets, characterized by a tubular block of synthetic material that accommodates the screw fixing and can be introduced into the drill made in the soft material, said block carrying on one of its ends a fungiform closed head. (Machine-translation by Google Translate, not legally binding)