Fire Door Thru-Bolt is used for holes up to 1/2″ in steel hollow fire rated doors. The Thru-Bolt is an aesthetically pleasing solution compared to unsightly normal bolts. The Fire Door Thru-Bolt is a simple male and female type application that is available in 1/4″ and 1/2″ widths for both 1-3/4″ and 2″ fire rated doors. The Fire Door Thru-Bolt meets the NFPA 80 18.104.22.168 requirements to protect your UL Label. Download our Fire Door Thru-Bolt Installation Instructions.