Shop Guide For Nuts Measure across flats size of nut,select the model corresponding to the inner hole diameter. Measure the length of the protruding screw under the nut and the nut,determine if the internal space of PE cap is enough. For external hexagon screws Measure the size of the head of the outer hexagon screw,select the model corrsponding to the inner hole diameter Effect as shown in the figure Prevent accidental injury caused by protruding parts of nuts and screws Waterproof and rust proof,reduce dust pollution and rain wash,extend the service life of screws and nuts