Trimco 3810X3850 Automatic Flushbolt (Metal Doors) w/Firebolt

The Trimco 3810 x 3850 is an automatic flush bolt set for the inactive leaf of a pair of metal doors, configured with the 3850 fire bolt replacing the bottom bolt. If you've been searching "trimco 3810", "trimco flush bolts", or "trimco 3820" - the 3810 is the automatic flush bolt for metal doors from Trimco's 3800 Series, and the 3850 is Trimco's UL fire bolt that mounts in the bottom position. The x in 3810 x 3850 means these two components are packaged and specified together as a matched set for a fire-rated inactive door leaf.

What Automatic Flush Bolts Do on a Pair of Doors

On a pair of doors, one leaf is the active leaf - the one with the primary lock that people use daily. The other is the inactive leaf, which stays closed most of the time and only opens when you need full-width access. The inactive leaf needs to be held closed at both top and bottom against the door frame. That's the flush bolt's job.

An automatic flush bolt shoots automatically when the inactive door leaf closes. As the door swings to the closed position, the bolt mechanism trips and the bolt extends into the frame at the top. No manual action required. This is different from a manual flush bolt, where someone has to reach down or up to manually slide the bolt into position after closing. Automatic is the correct specification for any inactive leaf that will be closed regularly without a person manually engaging it.

The 3820 is Trimco's semi-automatic flush bolt. Only one bolt in the set is automatic - the other requires manual operation. If both top and bottom need to engage automatically on door closing, the 3810 is the correct choice. If only the top bolt needs to auto-engage, the 3820 handles that configuration.

Trimco's Patented Design: Fewer Parts, Stainless Steel Core

The 3810 uses a patented mechanism with one-third fewer parts than conventional flush bolt designs. Key components are stainless steel. Fewer parts means fewer failure points and less maintenance over time. The operation is engineered to be extremely quiet - the bolt engages with low noise - and requires very low closing force to trigger the mechanism. On a high-traffic pair of doors where the inactive leaf gets bumped closed multiple times a day, a loud bolt that requires force to engage creates real operational issues. The 3810 addresses both problems at the design level, not just with installation technique.

The 3850 Fire Bolt: Fusible Membrane at 450 Degrees

The 3850 fire bolt replaces the bottom bolt in a 3810 auto flush bolt set. Under normal building conditions, the 3850 is held in the retracted position by a fusible membrane - the bolt is out of the way and the inactive leaf opens freely when needed. When a fire raises the temperature to 450 degrees Fahrenheit, the fusible membrane melts. Once it melts, the spring inside the 3850 drives the bolt forward, extending it into the bottom frame strike. This locks up the pair of doors mechanically at the bottom, preventing the inactive leaf from being forced open by fire pressure or thermal warping.

The 3850 is a thermal backup for the pair of doors - it doesn't operate during normal use, only during a fire event. It's required on fire-rated door pairs where code mandates that both leaves be secured against fire conditions even if the flush bolt mechanism itself fails or the door has been propped.

Specifications

Model: Trimco 3810 x 3850

Series: Trimco 3800 Series Automatic Flush Bolts

3810 Type: Automatic flush bolt for metal doors

3850 Type: UL fire bolt with fusible membrane, 450 degrees F activation

Operation: 3810 auto-engages on door closing; 3850 stays retracted until fire event

Semi-Automatic Version: 3820 (one bolt automatic only)

Wood Door Version: 3815L x 3850

Rod Length: 12" standard

Face Size: 1" x 6-3/4"

Construction: Stainless steel key components, patented fewer-parts design

Door Type: Metal doors

Application: Inactive leaf of fire-rated pair of doors

Finishes: 605, 606, 613, 613E, 622, 625, 626, 629, 630

UL Listed: Yes

American Locksets has stocked Trimco 3800 Series flush bolts since 2001.