Penta bolts have a five-sided pentagon-shaped head offering a minimum level of tamper-resistance. Penta head bolts are commonly used to secure ground lids and manhole covers. 18-8 stainless steel is functionally interchangeable with type 304 stainless steel. Stainless steel significantly improves resistance to tarnishing or corrosion.DIMENSIONAL ATTRIBUTES Diameter (Nominal): 1/2" Thread Pitch: 13 Length (Nominal): 1"PRODUCT ATTRIBUTES Category: Penta Bolts System of Measurement: Inch Brand: Aspen Fasteners® Head Style: Penta Head Drive Style: Tamper-Resistant External Pentagon Drive Thread Direction: Right-Hand Thread Material: Stainless Steel Material Grade: 18-8 Stainless Steel Coating: Uncoated