Rockwood 19BFB Bottom Fire Flush Bolt for Wood Door

That is exactly what it is for. The 19BFB is a bottom fire bolt for the inactive leaf of a pair of wood doors, and it eliminates both the bottom automatic flush bolt and the dust proof strike. The top of the leaf still gets an automatic top bolt, that is the half of the pair doing the everyday latching, but the bottom of the opening no longer needs a second automatic bolt or a strike in the floor.

UL Listed, with a condition attached: the 19BFB carries that listing only when it is used with an automatic top bolt. The two work as a set on the inactive leaf, the top bolt holding the door closed in normal use and the fire bolt sitting dormant at the bottom until heat reaches it. Run the fire bolt without the automatic top bolt and the UL Listing no longer covers the installation.

No, and that catches people out. A fire bolt stays retracted until heat reaches it. At 230 degrees F the plug and the black plastic cover melt, the bolt projects, and the leaves lock together. Day to day there is nothing holding the bottom of the inactive leaf, the automatic top bolt does that job. If you want a bolt someone can throw and release at the bottom of the door, the 19BFB is the wrong part and you want a manual or automatic bottom flush bolt instead.

It is built for wood doors. Like any flush bolt, the 19BFB mortises into the door itself, and the body and prep are cut for a wood leaf, so a hollow metal pair needs a bottom fire bolt made for metal doors instead. Same function, different prep. Check the leaf material before you order, because the two are not interchangeable in the field.

No floor strike goes with it. The 19BFB eliminates the dust proof strike along with the bottom automatic flush bolt, so there is no hole to core in the threshold or the slab and nothing in the floor to fill with grit. On a fire rated wood pair that is the practical draw: no floor prep, and no strike to realign when the doors settle.

It comes down to whether the bottom of the inactive leaf has to be held closed every day. An automatic bottom flush bolt latches each time the door closes and needs a dust proof strike in the floor to receive it. A bottom fire bolt like the Rockwood 19BFB does nothing until 230 degrees F, then the plug and cover melt and the bolt projects to lock the leaves together, and it takes the bottom automatic bolt and the floor strike out of the opening entirely. Automatic bolt at the top, fire bolt at the bottom is the combination the 19BFB is UL Listed with.

Heat triggers it at 230 degrees F. The bolt is held back by a plug and a black plastic cover, and at that temperature both melt so the bolt can project and lock the two leaves together, which keeps the pair acting as one unit against the fire. It is not a resettable device. Once the plug has melted, it has melted, so a 19BFB that has fired gets replaced rather than reset.

One finish, 630 satin stainless steel, in a stainless steel body. On US finish charts that is US32D, so if the balance of the openings is specified 630 or US32D it matches. Worth knowing that very little of a bottom fire bolt shows once it is installed, the unit is mortised into the leaf, so the finish matters mostly for consistency on the spec sheet rather than for what anyone sees walking past the doors.