PRODUCT SPECIFICATIONS Part #: 0000-180916 Fastener Type: Hex Flange Screw no Serration Size Description: 5/8-18 x 3 Diameter/Nominal Size: 5/8 Length: 3 Thread Pitch: 18 Thread Pitch Type: Fine Thread Direction: Right System of Measurement: Inch Grade: 8 Material: Alloy Steel Finish: Black Phosphate Head Type: Hex Flange Drive Type: External Hex Standards Met: SAE J429 Average Piece Weight: 0.3750000 lbs. Flange screws distributes holding pressure by having a circular shaped flange (external ridge) under the head so that the screw is less likely to come loose; non-serrated variety is also known as a frame bolt.