GB/T 800-1988

GB/T 800-1988 specifies the dimensions, technical requirements, and marking for flat countersunk double nib bolts, which feature a countersunk head and two nibs under the head to prevent rotation during assembly. This standard is applied in mechanical engineering and manufacturing contexts where bolts must be securely fastened into countersunk holes in metal or wood components, such as in automotive, agricultural machinery, or structural connections requiring a flush surface and anti-rotation locking. It ensures interchangeability and quality control for bolts used in applications where the bolt head must sit flush with the material surface while resisting loosening under vibration or torque.