With the widespread use of bi-fold doors in commercial buildings, high-end residences, and public spaces, the installation of flush bolts has become a focus of attention within the hardware and construction industries. Compared to traditional Surface Bolts, flush bolts are recessed into the edge of the door leaf, providing stability while also maintaining aesthetics and overall integrity.

Function of flush bolts in bi-fold doors

In a bi-fold door structure, one door leaf functions as the normally open leaf, while the other serves as the fixed leaf. Flush bolts are primarily used to secure the door leaf, ensuring the other leaf can open and close properly. Advantages include:

• Maintaining stability: Two points of anchorage prevent the fixed leaf from wobbling.

• Enhancing aesthetics: The flush design does not detract from the door's appearance.

• Easy operation: Locking and unlocking can be achieved by simply pushing or pulling a handle or slider.

Installation steps and technical tips

• Location: Select the upper and lower edges of the fixed leaf, typically 100–150 mm from the top and 200–250 mm from the bottom. Measuring and Notching: Use an electric milling machine or chisel to create a notch on the edge of the door leaf that matches the latch size, ensuring the correct depth and width.

• Installing the Latch: Insert the concealed latch into the notch, secure with screws, and check for smooth sliding.

• Drilling and Installing the Stitch Plate: Drill holes in the upper end of the door frame and the floor, and install a metal stitch plate or cover to ensure smooth latch insertion.

• Commissioning and Finishing: Perform repeated push-pull tests, fine-tuning the notch or stitch plate position as necessary to ensure smooth latch operation.

Installation Precautions

• High Precision Requirements: Excessive notching deviations can cause the latch to loosen or become stuck.

• Compliance Risks: Do not perform arbitrary installations on fire escape doors, as this may hinder escape.

• Material Selection: Stainless steel or high-strength alloys are recommended for durability and corrosion resistance.

Industry Trends and Innovation

With the increasing use of double-leaf doors, hardware manufacturers are introducing automatic-return concealed latches, integrated decorative designs, and electronic concealed latches that can be linked to smart access control systems. These products not only improve functionality, but also meet the needs of modern architecture for beauty and intelligence.