Suki Cup Square Screws feature a smooth, rounded ‘mushroom’ head with no external drive They have a square neck under the head which pulls into the material as the nuts are tightened, and prevents the bolt from turning once installed These carriage bolts can be used for fence construction and outdoor furniture They are generally pushed into a pre-drilled hole and then tightened in place with hex nuts or lock washers Steel construction Zinc-plated finish for corrosion resistance It conforms to the product standards of DIN 603