Continuous Gear Hinge Guide: Benefits, Types & Cross Reference
A continuous gear hinge consists of two full-height paired and geared leaves that rotate evenly from top to bottom on bearings, held together by a full-length channel cap. Unlike conventional butt hinges — and unlike piano hinges which have 50% of each knuckle cut away and rely on a thin wire — continuous gear hinges have no hinge pin and distribute load stress uniformly along the entire door height.
Why Choose Continuous Gear Hinges
Benefits over conventional door hinges
Eliminates door sag and binding
Load stress is distributed uniformly along the full door and frame height, eliminating wear from door closer kickback shock and preventing sag over time.
Easy operation on heavy doors
The gear design ensures identical operation of each leaf — very little effort is required to open even very heavy commercial doors.
Prevents door warpage
Fastening screws run along the full length of both leaves, preventing warpage of the door along the jamb.
Enhanced security
The full-length channel cap seals the gap between door and frame, providing resistance against prying and forced entry.
Safety & privacy
Closing the gap between door and frame prevents pinched fingers — ideal for schools and public buildings. The sight-proof design also provides privacy in lavatories, exam rooms, executive offices, and file rooms.
Bommer Continuous Gear Hinges are certified fully functional after 1.5 million cycles using a standard duty hinge and a 150 lb door — compared to some manufacturers who certify only 350,000 cycles using a heavy duty hinge and a 75 lb door. When you want the best, choose Bommer. Made in the USA.
Mounting Types
3 continuous gear hinge mounting configurations
Full Mortise
Designed primarily for new door installations. Both leaves are concealed — fastened into the door edge and frame jamb. Full mortise hinges will cover existing standard butt hinge mortises. Frame leaf fastened with #12-24 self-threading screws; door leaf fastened to door edge with #12-24 self-threading screws. Use #12 wood screws for wood doors or frames.
Full Surface
Designed for renovations and retrofitting. Both leaves are surface mounted to the exposed door and frame faces. The hinge-side gap clearance can be as narrow as 1/16", keeping the latch-side gap consistent with previous hardware. Frame leaf fastened with #12-24 screws; door leaf fastened with ¼"-20 thru-bolts and #12-24 screws. Use #12 wood screws for wood applications.
Half Surface
Designed for renovations and retrofitting. The door leaf is surface mounted to the exposed door face; the frame leaf is concealed in the frame jamb. Half surface hinges will cover existing standard hinge preps. Frame leaf fastened with #12-24 screws; door leaf fastened with ¼"-20 thru-bolts and #12-24 screws. Use #12 wood screws for wood applications.
Cross Reference
Continuous gear hinge cross reference chart
Use this chart to find equivalent models across Bommer, Hager-Roton, and MontHard. Note: products from different manufacturers may not be identical.
| Description | Bommer | Hager-Roton | MontHard |
|---|---|---|---|
| 83" Standard Full Mortise, Heavy Duty | FM83HD | 780-224HD, 83" | THI-1183FM2HD |
| 85" Standard Full Mortise, Heavy Duty | FM85HD | 780-224HD, 85" | — |
| 95" Standard Full Mortise, Heavy Duty | FM95HD | 780-224HD, 95" | THI-1195FM2HD |
| 120" Standard Full Mortise, Heavy Duty | FM120HD | 780-224HD, 120" | — |
| 83" Full Mortise, Flush, Heavy Duty | FM83SLF-HD | 780-112HD, 83" | THI-1183CFMHD |
| 85" Full Mortise, Flush, Heavy Duty | FM85SLF-HD | 780-112HD, 85" | — |
| 95" Full Mortise, Flush, Heavy Duty | FM95SLF-HD | 780-112HD, 95" | THI-1195CFMHD |
| 120" Full Mortise, Flush, Heavy Duty | FM120SLF-HD | 780-112HD, 120" | — |
| 83" Full Mortise, Inset, Heavy Duty | FM83SLI-HD | — | THI-1183FM2HD |
| 85" Full Mortise, Inset, Heavy Duty | FM85SLF-HD | — | — |
| 95" Full Mortise, Inset, Heavy Duty | FM95SLF-HD | — | THI-1195FM2HD |
| 120" Full Mortise, Inset, Heavy Duty | FM120SLF-HD | — | — |
| 83" Full Surface, Heavy Duty | FS83HD | 780-210HD, 83" | THI-1183HD |
| 85" Full Surface, Heavy Duty | FS85HD | 780-210HD, 85" | — |
| 95" Full Surface, Heavy Duty | FS95HD | 780-210HD, 95" | THI-1195HD |
| 120" Full Surface, Heavy Duty | FS120HD | 780-210HD, 120" | — |
| 83" Full Surface, Narrow Frame, Heavy Duty | — | 780-157HD, 83" | THI-1183LFHD |
| 95" Full Surface, Narrow Frame, Heavy Duty | — | 780-157HD, 95" | THI-1195LFHD |
| 83" Half Surface, Heavy Duty | HS83HD | 780-054HD, 83" | — |
| 85" Half Surface, Heavy Duty | HS85HD | 780-054HD, 85" | — |
| 95" Half Surface, Heavy Duty | HS95HD | 780-054HD, 95" | — |
| 120" Half Surface, Heavy Duty | HS120HD | 780-054HD, 120" | — |
Need help choosing?
Not sure which continuous gear hinge is right for your door? Contact us with your door dimensions and application. Browse our full continuous gear hinge collection or return to the Help Center.